Hello, Codeforces!

I am glad to invite you to take part in Codeforces Round #577 (Div 2), which will be held on Sunday, 4 August at 16:35 UTC.

You will be given 5 problems, one of them will have 2 subtasks and 2 hours to solve them.

The round will be rated for the second division.

Huge thanks to cdkrot and KAN for helping to prepare the round.

I would like to thank to 300iq, isaf27, vintage_Vlad_Makeev, pllk, mohammedehab2002, 74TrAkToR, Rox, _overrated_ for testing the round.

And thanks to MikeMirzayanov for the great codeforces and polygon platforms.

This is my first Codeforces round. Hope you will enjoy it.

Good luck and have fun!

UPD: The scoring distribution is: 500 — 1000 — 1500 — 2000 — (2000 + 1000)

UPD2: Editorial

UPD3: Congratulations to the winners:

Div2:

1: wwaynetuu

2: jerome_mei

3: satu0king

4: Yazmau

5: Tlatoani, Hasan0540, boba5551

Unofficial Div1:

1: neal

2: uwi

3: scott_wu

4: I_love_Tanya_Romanova

5: ecnerwala

Hello!

I'm glad to invite you all to Round 576 which will take place on Jul/30/2019 17:35 (Moscow time).

There will be 6 problem in both divisions.

Round is based on Team Olympiad in Computer Science Summer School. It is (yet another) summer school for schoolchildren organized by Higher School of Economics and "Strategy" Center in Lipetsk. Almost all the problems are authored and prepared by teachers and teaching assistants in CSSS: Um_nik, Burunduk1, fake123_loves_me, MakArtKar, Villen3tenmerth, Aphanasiy, Gadget. One of the problems is authored by Merkurev (just because we are friends :) ). One more problem for the round was added by KAN.

I would like to thank KAN for CF round coordination, I_love_Tanya_Romanova, Merkurev, Rox and 74TrAkToR for testing, and Codeforces and Polygon team for these beautiful platforms.

Scoring will be announced.

Upd: We added one more problem to div.1 contest, now both contests have 6 problems (4 in common). The round is not combined, if it were, I would write "combined" in the title.

Scoring distribution:
div2: 500-750-1250-1750-2500-3000
div1: 500-750-1250-1500-1750-2250

Congratulations to our winners!
div.1:
1. Radewoosh
2. tourist
3. mnbvmar
4. Benq
5. pashka
div.2:
1. ChthollyNotaSeniorious
2. Honour_34
3. idxcalcal
4. shogunator
5. yijan

Editorial won't be published.

The 26th Central European Olympiad in Informatics will take place in Bratislava, Slovakia, during July 23rd-29th 2019. The most gifted high school students from 13 countries will have the opportunity to prove their knowledge and skills in informatics.

Codeforces will organise the online mirror for this year's competition. The online mirrors will take place after the finish of each of the 2 competition days, having the same scoring format.

The online mirror schedules are the following:

• Jul/25/2019 17:05 (Moscow time)
• Jul/28/2019 11:05 (Moscow time)

Contest format

• The contest will be unrated for all users.
• You will have to solve 3 tasks in 5 hours.
• There will be full feedback throughout the entire contest.
• The scoreboard will be hidden until the end of the contest.
• The tasks will have partial scoring. The maximum score for each problem will be 100 points.
• Among multiple submissions only the one that achieves the maximum score is counted towards the final ranking.
• The submission time does not matter for ranking.
• There will be enough fun for all colours ranging from newbie to international grandmaster. Legendary grandmasters can spice it up by turning it into a drinking game (ask Radewoosh for details).

Link to onsite contest with official rules and scoreboard

UPDATE: Much nicer scoreboard than on the first day made by arsijo. Many thanks!

Congratulations to all onsite contestants who battled our unusually hard problemset for 10 hours. You can view the final standings.

Many thanks to KAN for running the mirror, MikeMirzayanov for both platforms, all of our authors, testers and the whole CEOI staff and sponsors!

Day 1 mirror:

1. mnbvmar 300
2. Benq 300
3. gamegame 281
4. ainta 271
5. Tutis 254

Day 2 mirror:

1. zx2003 230
2. saba2000 230
3. TLE 200
4. cuizhuyefei 200
5. panole 200
6. dacin21 200

Results of both days combined: (https://codeforces.com/spectator/ranklist/e354b9b95c3626a3cfdfdb9eb37a7a6f)

Editorials: day1 day2

<almost-copy-pasted-part>

Hello! Codeforces Round 575 (Div. 3) will start at Jul/24/2019 17:35 (Moscow time). You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 or 7 (or 8) problems and 2 hours to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participants of the third division, you must:

• take part in at least two rated rounds (and solve at least one problem in each of them),
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of my work. Thanks to my good friends Mikhail awoo Piklyaev, Maksim Neon Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

I also would like to say that participants who will submit wrong solutions on purpose and hack them afterwards (example) will not be shown in the hacking leaders table.

</almost-copy-pasted-part>

UPD: I also would like to thank Ivan BledDest Androsov for help with problems preparation, and also danya.smelskiy, greencis, chenjb and STommydx for testing the round!

UPD2: Editorial is published!

UPD3: I also would like to thank my friend Maksim Neon Mescheryakov for improving tests of the problem F! :D

Hello Codeforces!

On Jul/22/2019 17:35 (Moscow time) Educational Codeforces Round 69 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 problems and 2 hours to solve them.

The problems were invented and prepared by Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all participants!

UPD: Our friends at Harbour.Space also have a message for you:

Hello Codeforces!

We hope your summer is going well!

Last Friday we finished the second edition of the Tech Scouts Summer Camp, with 70 participants, 20 different nationalities and many solved problems. We had 6 participants with a full scholarship thanks to the collaboration between Harbour.Space and Codeforces and we are working on increasing this number next year.

We would also like to remind you that we offer scholarships for our technical programmes, such as Computer Science, Data Science and Cyber Security.

They are set in such a way that doesn’t require additional applications — we believe in merit and potential, and so what you put in your application to the university will be our criteria.

You could be just the diamond we’re looking for, but you’ll never know unless you apply!

UPD2: There will be 6 problems in the contest.

Congratulations to the winners:

Congratulations to the best hackers:

And finally people who were the first to solve each problem:

UPD3: Editorial is out

Hi!

On Jul/20/2019 18:35 (Moscow time) we will host Codeforces Global Round 4.

It is the fourth round of a new series of Codeforces Global Rounds supported by XTX Markets. The rounds are open for everybody, the rating will be updated for everybody.

You will be given 8 problems and 150 minutes to solve them. The scoring distribution will be 500-750-1250-1750-2000-(1500+1500)+3250+4000.

The prizes for this round:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2019:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over the whole series get sweatshirts and place certificates.

The problems of this round were developed by me. I will be available on Discord to discuss the problems after the contest.

I would like to thank:

• arsijo for his help in the round's coordination,
• 300iq, Aleks5d, arsijo, Ashishgup, Jeel_Vaishnav, Khairy, cdkrot, ksun48, Learner99, Noam527, stanislav.bezkorovainyi, TonySnark, Um_nik for testing the round,
• MikeMirzayanov for Codeforces and Polygon,
• Pretest for being so strong, TLE for being so rare, system_test for being so fast and Editorial for being ready right after the contest finishes.

UPD: The round is finished. I hope you enjoyed the problems! I am very sorry about the issue on E.

UPD2: Editorial

UPD3: Congratulations to:

1. ainta
2. Radewoosh
3. tzuyu_chou
4. LHiC
5. Benq

UPD4: The results after four rounds.

Hi everyone! I'm glad to invite all of you to participate in Codeforces Round 574 (Div. 2) which will take a place in Jul/17/2019 17:35 (Moscow time).

This round is based on SIS team contest. You will be given 6 problems and 2 hours to solve them. This round will be rated for Div. 2 participants. In other words, this round will be rated for the participants with rating lower than 2100. As usual, participants from the first division are welcome to join out of competition.

Problems was invented and prepared by budalnik, Kurpilyansky, meshanya, tsarn, sava-cska, ima_ima_go and craborac. I am just a coordinator of this round, I made a small amount of work such as English translations and editorials. I want to thank Mikhail MikeMirzayanov Mirzayanov for amazing systems Codeforces and Polygon, all authors of this great contest, KAN and cdkrot for help with difficulties estimating and choosing the problems and my dear friend Ivan BledDest Androsov for help with round preparation!

Good luck everyone and see only green system testing messages! :)

UPD: The scoring is 500 — 1000 — 1500 — (1000+1500) — 3000 — 3500.

UPD2: I would like to thank testers galloska, NatInTheHat and AlexPop28 for help and advices about the round!

UPD3: Editorial is published!

Hello Codeforces!

On Jul/14/2019 17:45 (Moscow time) Educational Codeforces Round 68 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 7 problems and 2 hours to solve them.

The problems were invented and prepared by Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all participants!

Congratulations to the winners:

Congratulations to the best hackers:

And finally people who were the first to solve each problem:

UPD: Editorial is out

What do you do on Friday evening? Are you busy? Will you take part in our round?

Hello, Codeforces!

We are glad to invite you to take part in Codeforces Round 573 (Div. 1) and Codeforces Round 573 (Div. 2), which will be held on Jul/12/2019 17:35 (Moscow time).

The round will be rated for all participants from both divisions.Participants in each division will be offered 6 problems and 2 hours (to be determined) to solve them. Both divisions will share 4 problems.

The problems were written and prepared by 2014CAIS01, tender, teitoku, winterzz1, chenjb, Subconscious, Claris, quailty, skywalkert and me.

Thank to:

• tender for providing stories for some problems.

• skywalkert, Claris, quailty, WhaleVomit, NIWIS, WolfBlue and isaf27 for testing this round and giving good advice.

• skywalkert for helping me to prepare and translate the statement and tutorial (and sorry for my poor English (╥﹏╥) ).

• scanhex for helping us to translate the statement to Russian.

• 300iq, KAN and MikeMirzayanov for excellent coordination of this round!

• MikeMirzayanov and his Codeforces team for amazing systems Codeforces and Polygon! (I like Codeforces forever! )

If you are not busy, please take part in our round on Friday evening! We wish you good luck and high rating!

The score distribution will soon be published.

UPD1: Some of authors will be at the Discord CP Community to discuss the problems after the coding phase. However, please follow the rules and don't discuss the problems before or during the contest by any means.

UPD2: List of contributors is a bit changed, and the scoring distribution will be:

• Div.2: 500 — 1000 — 1500 — 2000 — 2500 — 2500

• Div.1: 500 — 1000 — 1500 — 1500 — 2250 — 2750

UPD3: Sorry for forcing you to spell our nicknames, 'tokitsukaze' and 'quailty', and some ambiguity in the statements. Anyway, we sincerely appreciate your participation.

UPD4: Editorial

UPD5: Congratulations to the winners!

Div.1:

1. Um_nik

2. Benq

3. ATS

4. tmwilliamlin168

5. wiwitrifai

Div.2:

1. RannRu

2. cyy233cnbb

3. AnandOza

4. puppies_and_rainbows

5. calabash_fool