Good morning/afternoon/evening, Codeforcers!

We (Nezzar, triple__a, Nanako) are very excited to present to you Codeforces Round #698 (Div. 1) and Codeforces Round #698 (Div. 2), which will take place in Jan/28/2021 17:35 (Moscow time).

There will be 6 tasks waiting for you to be solved in 135 minutes!

We would also want to thank:

• isaf27 for the coordination and discussion of this round!

• KAN for great help and advice of round prepartion!

• alex20030190, KAN, Roundgod, gisp_zjz, sshwyR, xryjr233, jhdonghj112, low_, dragon_bra, gamegame, mmello, cycl, Reiva5, kzyKT, hitonanode, parker0523, baohiep for testing and providing valuable feedback of the problems!

• MikeMirzayanov for great systems Codeforces and Polygon!

Score distribution will be announced at $$$n$$$ $$$(0 \leq n < + \infty)$$$ minutes before round starts.

We hope you high performance with a lot of points earned during contest!

Hello Codeforces!

It's been a long time since I posted a lesson in EDU section. Sorry about that, was quite busy managing my course on Youtube.

New lesson is about two pointers method.

What topics you want to learn next? I would prefer topics not covered in my Youtube course, something more specific for competetive programming. Any ideas?

More about EDU section you can read in this post.

Thanks to Stepavly and Supermagzzz for their help with lecture notes and testing problems.

Enjoy the lesson and good luck on the contests!

Hello, Codeforces! Were you afraid of the lack of contests? We also!

Unfortunately, due to technical problems, the round is declared unrated. You can continue to solve problems, but the results of the current round will not affect your rating. We are sorry for this situation.

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Hello! Codeforces Round #697 (Div. 3) will start at Jan/25/2021 18:00 (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. 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 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 me Supermagzzz and Stepavly

Thanks to MikeMirzayanov for platforms and coordination of our work. Thanks to darkkcyan, Tzak, bfs.07, songsinger, iankury, spookywooky, Programmer, sodafago, infinitepro for help in round preparation and testing the round.

Good luck!

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UPD: Editorial is ready!

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 is $$$500-1000-1500-2000-2250-3000$$$.

Good luck!

UPD: Editorial

UPD: Congratulations to the winners!

Of both divisions:

1. neal

2. antontrygubO_o

3. HIR180

4. fuppy

5. Thienu

Of the second division:

1. EzioAuditoreDaFirenze

2. Ishtar

3. God_Of_Blunder

4. Shivam_18

5. AlphaAurigae

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.