Hi, Everyone!

At Jan/20/2019 15:05 (Moscow time) will start Codeforces Round #533 (Div. 2). Round will be rated for second division (rating below 2100). As usual, participants from the first division can participate in the contest out of competition.

The round will consist of 5 problems in which you will be helping some of my friends and you will be given two hours to help them.

I would like to thank MikeMirzayanov for the Codeforces and Polygon platforms, _kun_ for round coordination and help with preparation. Also thanks to V--gLaSsH0ldEr593--V, Aleks5d,Nebuchadnezzar, Arpa, mohammedehab2002 and osaaateiasavtnl. for help with preparation and testing round.

As usual score distribution will be announced shortly before the contest.

Good luck!

UPD1: I'll be on the Discord channel after the contest, so we will be able to discuss the problems.

UPD2: Score distribution : 500-1000-1500-2000-2500

Hi, Codeforces!

At Jan/13/2019 17:35 (Moscow time) will start Codeforces Round #532 (Div. 2). Round will be rated for second division (rating below 2100). As usual, participants from the first division can participate in a contest out of competition.

The round will consist of 6 problems and you will be given two hours to solve them.

Task prepared by me, den2204.

Thanks MikeMirzayanov for the platform Codeforces, KAN for round coordination and help with preparation. Thanks gritukan, Andreikkaa, flyrise, Um_nik, Aleks5d and osaaateiasavtnl. for help with preparation and testing round, arsor for translating statements into English, arsijo for assistance in conducting the round. Thanks Andreikkaa for the idea of the problem E.

Good luck!

P.S. It is my first round on Codeforces, please, do not judge strictly :)

UPD: Added editorial. Thank you all for participating and for the feedback on the contest. I apologize for the leap in complexity between tasks and for weak pretests for some tasks, I’ll take this into account when further preparing contests.

Hello Codeforces!

On Jan/11/2019 17:35 (Moscow time) Educational Codeforces Round 58 (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 extented ACM 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, Grigory V--gLaSsH0ldEr593--V Reznikov and me.

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: The editorial is out

Happy New Year to all of you! So, meet another round from blue :)

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Hello!

Codeforces Round #531 (Div. 3) will start at Jan/09/2019 17:35 (Moscow time). You will be offered 6 or 7 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. 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 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 PikMike Piklyaev, Maksim Ne0n25 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.

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UPD1:

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD2: Editorial is published!

UPD3: I forgot to thank eddy1021 for help with testing the round!

Hello everybody!

Now the winter SIS (Summer Informatics School) is taking place, and we, as part of the parallel A+ with its teachers, have prepared a complete Codeforces Round.

The round will happen at Jan/05/2019 19:35 (Moscow time) and will last for 2.5 hours. There will be 6 problems in each division.

The tasks of the round were invented and prepared by 300iq, scanhex, cookiedoth, allrats, osaaateiasavtnl., Qlukva, Forestryks, Dimon, LordVoldebug, romanovsavelij, golub, ismagilov.code,alexey_kuldoshin, LadyPython, UnstoppableSolveMachine under the guidance of teachers izban, VArtem, _meshanya_, pashka.

Also thanks for testing isaf27, isaf27_loves_me, Kurpilyansky.

And, of course, thanks to MikeMirzayanov for great systems Codeforces and Polygon.

Good luck everybody!

UPD: Since the registration opens before the recalculation of the rating after Hello 2019, in case of a division change, the participants will be moved to another division.

UPD: Editorial.

Hello coders! I hope that you are enjoying the New Year as much as me. To make its beginning even greater, Codeforces is going to host a contest and I will be an author of all tasks. Hello 2019 will take place on Friday.

Using the opportunity, I want to thank to:

• lewin and mnbvmar for testing the round.
• mnbvmar for indescribably helpful discussions about problems.
• _kun_ and KAN for round coordination and help with preparation.
• MikeMirzayanov for such great platforms (you know which ones :P).

The round will consist of 8 problems and you will be given two and a half three hours to solve them. Yes, the round will be rated.

There will be no interactive problems, but if you want you can read this document anyway, it's always good to learn new things.

Good luck and see you during the contest!

UPD1: Editorial

UPD2: I'll be on the Discord channel after the contest, so you will be able to ask me about the problems.

UPD3: You're probably wondering what the statements will be about. I hope that it will be another great year for Codeforces. As it's the community that creates it, I decided to write statements about the people who already have or had their part in Codeforces' history. As I wanted to be objective, the statements will be about 8 people who triumphed the most times in CF rounds. Using the opportunity, I want to invite these 8 people to take part in the contest. Let's say that the first person who will guess the set in the comments wins some free contribution. Good luck!

UPD4: The round will be 3 hours long.

UPD5: The drain will be adjusted and the scoring will be 500-1000-1500-2000-2750-3000-3500-4000.

UPD6: The round is over, congratulations to the winners!

1. V--o_o--V
2. ecnerwala
3. tourist
4. lych_cys
5. Petr

And to the first-to-solvers!

• A: Errichto
• B: dorijanlendvaj
• C: Um_nik
• D: rng_58 (his personal task!)
• E: LHIC
• F: tourist
• G: V--o_o--V (his personal task!)
• H: ecnerwala

UPD7: Editorial

Congratulations to all the new 2019 year! At this very moment you can make an important wish. Done? I wish it to be fulfilled!

I wish you to become better in the new year, to think better and to meet less often with bugs and mistakes. Let all your solutions be fast, effective and correct!

Later, I will compile statistics for 2018 and publish in the form of an annual report

Now I'd like to remind you most voted posts of 2018. Here is the list of the top 15:

• Codeforces: Problem Difficulties by me, +3158
• Codeforces: Our Steps After DDOS Attack me, +2995
• Hello 2018 by tourist, +2848
• Codeforces: Updates in rating and rounds by me, +1973
• Blogewoosh #1 by Radewoosh, +1798
• Linear Recurrence and Berlekamp-Massey Algorithm by TLE, +1492
• Hello, ITMO! by me, +1331
• Codeforces: Results of 2017 by me, +1319
• Should I start writing regular blogs? by Radewoosh, +1083
• Blogewoosh #6 by Radewoosh, +1075
• Multiple accounts for one person should be banned by dotorya, +1047
• Retiring from rated contests by bmerry, +1038
• Good Bye 2018 by majk, +985
• Stream by Errichto, +973
• Teams going to ACM ICPC World Finals 2018 by Luqman, +938

Happy New Year!

Do you already have a New Year's mood?

And we have traditional gifts!

Change Handle Feature

Hurry! Only until the 10th of January, you can change your handle (but only once)! Note that it will be possible to roll back the changes or change the handle again only after a year. Be careful what you wish for.

You can change your handle to the new one which wasn't used before by anybody or which was used by you before. The links to a profile page with old handle would automatically redirect to the actual profile.

This year we have an improvement. If you took part in at least 10 rounds you can request handle of an inactive participant. It means that the participant should have a period of activity on Codeforces of at most 90 days, this period should be in 2015 or earlier. The inactive participant can’t have posted comments, messages and so on. It can't take part in more than 2 contests. It will be automatically renamed and informed by email. If you can’t change handle to others, it means that some requirement doesn't meet. Please do not ask me to do something with it. I'm not Santa Claus.

Talking about handles I always reminisce the following story. Once a user wrote me the message: "Please change my handle from I_love_Valya to I_love_Sveta, as I no longer love Valya ..."

New Year's Masquerade of Colors and Ranks

Traditional magical tab has appeared in the profile setting. Happy New Year!

The end of the December is fast approaching and it is time for the best last contest of the year! The Good Bye 2018 round will take place on Sunday, December 30, 2018 at 14:35 UTC.

As the people who already engaged in discussions about the ultimate problem suspect, I am the problem writer. As such, I'd like to thank to:

• arsijo and KAN for the round coordination and one of the problems,
• AlexFetisov, cyand1317, Errichto, Jeel_Vaishnav, lewin, misof, winger for testing and invaluable suggestions,
• MikeMirzayanov and everyone involved in building and running Codeforces and Polygon platform.

The round will last for 2:30 hours and you will be given 8 problems for both divisions. There will be an interactive problem.

You have the last opportunity to reach Your rating goals for 2018. Good luck!

UPD: The top 3 participants eligible for ICPC 2019/20 season can win a great prize.

UPD2: The scoring distribution is 500-1000-1750-2250-3000-3000-3750-4000.

UPD3: Round is finished. I hope you enjoyed the contest! I am really sorry for the duck-up in problem G. I'll share more details once the important things (systest, editorial ...) are taken care of. The systest might be slightly delayed because of that.

UPD4: Editorial

UPD5: We apologize for the issue with problem G. We are still investigating this issue. Verdicts “Idleness limit exceeded” may be changed to other. We will write a full report about it later.

UPD6: The results are final, rating will be recalculated shortly. Congratulations to the winners:

1. tourist
2. MakeRussiaGreatAgain
3. Um_nik
4. ecnerwala
5. Radewoosh

UPD7: Some more information about problem G