Hi, Codeforces!

I'm glad to invite you to take part in Codeforces Round #696, which will take place on Jan/19/2021 17:35 (Moscow time). Round will be rated for participants with rating less than $$$2100$$$. Participants from the first division can take part out of competition.

There will be $$$6$$$ problems for $$$2$$$ hours. All problems are authored by me. Thanks to adedalic for excellent round coordination and to MikeMirzayanov for Codeforces and Polygon.

Also thanks to testers errorgorn, awoo, rkm62, khiro, AmShZ, IaMaNanBord, Osama_Alkhodairy, Prakash11, Gauravvv, HIS_GRACE, Dragnoid99 for testing the round and giving valuable feedback for problems.

Scoring will be announced before the contest.

Good luck!

Hello Codeforces!

On Jan/14/2021 17:35 (Moscow time) Educational Codeforces Round 102 (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 or 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 the participants!

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

Hey Codeforces and Happy New Year!

To kick off 2021, we want to introduce you to new opportunities!

Undoubtedly, Harbour.Space is always happy to see Codeforces participants among our students! Young talents who are eager to learn, challenge themselves, seek continuous development are our top priority.

That’s why we want to announce our amazing apprenticeship program.

Our mission is to spark positive impact cycles between promising young talent, the tech industry, and innovative educators. We continuously work on finding the perfect match between talent and companies.

Check out a success story from one of our first apprenticeship program students.

David is a UX/UI specialist from Georgia who received a full scholarship from venture capital fund, OneRagtime.

But there are plenty more apprenticeship opportunities coming in the fields of technology, entrepreneurship, and design. Interested? Keep in touch and follow us on LinkedIn for more fantastic opportunities.

Good luck on your round, and see you next time!

Harbour.Space University

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD: Editorial is out

Hello everyone!

The Codeforces team is working hard every day to improve the platform. Here's a quick overview of the latest innovations.

Mashups deletion

Until recently, there was no way on Codeforces to completely remove mashups you created. They stayed "hanging" in the interface and could get in the way if there were a lot of them.

Now you can delete the mashups you created. To do this, go to the edit page:

At the bottom of the page there will be a delete button:

Deleting a mashup is reversible, meaning you can restore it if necessary. You can view deleted mashups by clicking on the link below the table with mashups.

Other innovations

• Added filter by contest format (IOI or ICPC) in mashups and gyms.
• Compiler versions updated: Python 2 up to 2.7.18, Python 3 up to 3.9.1, Ruby up to 3.0.0, Go up to 1.15.6, Rust up to 1.49.0.
• Now you can hide streams from the calendar.
• The page with the list of user's contests now shows when the contest started.
• The group invites page now shows who invited you.
• Now you can massively change problem indices in mashups. Previously, to renumber problems in the mashup, you had to edit each task separately.

Hello Codeforces!

I am pleased to invite you to my first contest Codeforces Round #695 (Div. 2), which will take place on 08.01.2021 17:35 (Московское время). The problems were written by alimq and DS007. The round is rated for all users with rating less than 2100, while other users can participate unofficially.

You will be given 5 problems and 2 hours to solve them. You are strongly advised to read all the problems.

I would really like to thank:

• BledDest for his amazing coordination of the round.
• Aggu_01000101 and infinitepro for helping me in shortening the problem statements and solving one of the problems.
• MikeMirzayanov for creating the Codeforces and Polygon systems.
• The following people for testing the round:

We hope you will enjoy the problem set! Good luck!

The scoring distribution will be added shortly.

UPD: Also thanks to nooinenoojno for testing the round.

UPD: The scoring distribution is: $$$500 - 1000 - 1500 - 1750 - 2500$$$.

UPD: Congratulations to the winners

Of div 1:
1. kort0n
2. Suiseiseki
3. peti1234
4. fastmath
5. wrinx

And of div 2:
1. raingirl
2. xsdns
3. Mister5
4. o.a
5. wudi2016

Thank you all for participating! My apologies for misjudging the difficulty of B.
Editorial

Hello Codeforces!

Now the winter SIS (Summer Informatics School) is taking place, and parallel A+A0 and its teachers have prepared a complete Codeforces Round. You can check previous rounds, prepared by SIS students: Codeforces Round #612, Codeforces Round #530.

Codeforces Round #694 begins on Jan/05/2021 17:35 (Moscow time). In both redactions, there will be $$$6$$$ problems for $$$2$$$ hours. The round is rated for both divisions.

Problems are authored and prepared by AliceG, Pakhomovee, MadProgrammer, ArtNext, fastmath, IgorI, Kapt, KhB, Hello_zoka, Karabutsa, Arbuzniy_kekich, Mangooste, pelmenner, Allvik06 under the guidance of meshanya, cdkrot, kokokostya, kraborak, scanhex.

We would like to thank:

• 300iq for round coordination.

• MikeMirzayanov for Polygon and Codeforces.

• LHiC, Nebuchadnezzar, KAN, 1-gon, IaMaNanBord, ld_minh4354, Gauravvv, Vergara for testing the round and giving useful feedback.

We recommend you to read the statements of all problems. Scoring will be announced later.

Good luck!

Scoring distribution is: $$$500 - 750 - 1000 - 1500 - 2000 - 2500$$$ in both divisions.

Editorial

System testing is over. Thank you for participating! We hope that you liked our problems!

Congratulations to the winners:

1. tourist

2. Petr

3. jiangly

4. Radewoosh

5. ecnerwala

6. Maksim1744

7. lumibons

8. Endagorion

9. ainta

10. DmitryGrigorev

11. neal

All of them have solved problem E (with neal being the first). Problem F was quite challenging and no one have solved it during the contest.

Happy New Year, Codeforces!

UPD: We have received such different opinions about the order of problems, that we cannot be completely sure about it. We recommend you to read all the problems and do not strongly hope that the difficulty for you necessarily coincides with the order in the round.

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Hello! Codeforces Round #693 (Div. 3) will start at Jan/04/2021 17:35 (Moscow time). You will be offered 7 problems 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 a rating 1600 or higher, can register for the round unofficially. The round will be hosted by rules of educational rounds (extended 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. We tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 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 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.

The problems for this round were invented by MikeMirzayanov and prepared by Supermagzzz and Stepavly

Thanks to MikeMirzayanov for platforms and coordination of our work. Thanks to darkkcyan, Aris_244_, Mukundan314, PrideBlack, Nemo, pashka, Rox for help in round preparation and testing the round.

Good luck!

</almost-copy-pasted-part>

UPD: Editorial

Hello Codeforces!

This unusual and difficult 2020 has come to an end! What will the new year be like? I wish all of us that we have the opportunity to meet in person so that the contests take place not only online. I ask you to think of something important and good. Let this wish come true!

We have had a large number of rounds this year. I hope we have pleased you with interesting problems. Thanks to the round coordinators and writers! You make our community richer. Please make us happy in 2021!

I wish the participants victories over yourself (and over problems!) and development of your skills, interest and curiosity!

Hello, 2021!

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 an old handle would automatically redirect to the actual profile.

Again, this year if you took part in at least 10 rounds you can request a handle of an inactive participant. It means that the participant should have a period of activity on Codeforces of at most 180 days, this period should be in 2017 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. A user has the opportunity to request back his/her handle: in this case, we will roll back the change and return your previous handle to you. If you can't change your handle to another, it means that some requirement doesn't meet. Please do not ask me to do something with it. Especially, I do not like requests like "this is my second account, I took an interesting handle myself". 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

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

— MikeMirzayanov

Hello Codeforces!

We have a pleasure to invite you to Good Bye 2020, which will take place on Dec/30/2020 17:35 (Moscow time). You will have 3 hours to solve 9 problems. The round will be rated for participants of both divisions.

The problems for this round were prepared by gawry, Anadi and me.

We would like to thank everyone who made this round possible:

• Nebuchadnezzar and KAN for the excellent coordination;

• Omkar, 221, Manik, namanbansal013, prabowo, Saurabh_yadav, Gauravvv, Fly_37, Thaid, rkm62, neverblunder, Shinchan01, LazyPrime, Jellyman102, SecondThread, Origenes, PS41, antontrygubO_o, yarek and Rzepa for taking the time to test and providing useful feedback;

• MikeMirzayanov for great platforms Codeforces and Polygon.

We hope you will enjoy the problem set! Good luck!

UPD: Score distribution: $$$500$$$ $$$-$$$ $$$750$$$ $$$-$$$ $$$1000$$$ $$$-$$$ $$$1000$$$ $$$-$$$ $$$1500$$$ $$$-$$$ $$$1750$$$ $$$-$$$ $$$2500$$$ $$$-$$$ $$$3500$$$ $$$-$$$ $$$4000$$$

UPD: Editorial

UPD: Congratulations to the winners!

1. tourist
2. maroonrk
3. Benq
4. scott_wu
5. fivedemands
6. Um_nik
7. mnbvmar
8. heno239
9. aid
10. ainta

Hello Codeforces!

On Dec/28/2020 17:35 (Moscow time) Educational Codeforces Round 101 (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 or 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 the 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