Hello again, Codeforces!

I am glad to invite you to Codeforces Round 1004 (Div. 1), Codeforces Round 1004 (Div. 2), at Feb/11/2025 17:35 (Moscow time).

In Division 1 you will be offered $$$6$$$ problems. In Division 2 you will be offered $$$7$$$ problems. One of the problems in Div.1 will be divided into 2 subtasks. Round duration is set to be 2 hours.

Also, both divisions contain at least one interactive problem(s), so be prepared for those! Guide for interactive problems

I would like to thank,

• FairyWinx for dedicated coordination, a lot of problemset discussion, and suggesting one of the problems idea.

• Our testers: Dart-Xeyter, I_love_kirill22, RP-1, larush, Wansur, furt1ve, Iura_Shch, SomethingNew, Gabbasov, glllll, domovonok, Error_Yuan, Monogon, triple__a, evjeny_23, Blinov_Artemii, LeoPro, antontrygubO_o, A_G, N_z__, mainyutin for testing and providing feedback.

• MikeMirzayanov, KAN for Polygon and Codeforces platforms.

As always, we hope you will like the problems. Have fun!

Score Distribution:

Div. 1: $$$750$$$ — $$$750$$$ — $$$1250$$$ — ($$$750$$$ + $$$1250$$$) — $$$2000$$$ — $$$3000$$$

Div. 2: $$$500$$$ — $$$1000$$$ — $$$1250$$$ — $$$1750$$$ — $$$1750$$$ — $$$2250$$$ — $$$3000$$$

UPD: Editorial

UPD2: We sincerely regret to inform you that we have discovered a bug in the interactor. A series of tests is currently underway to assess the full impact of this issue. Once we have the results, we will provide a detailed update. We deeply apologize for this incident and any inconvenience it may have caused.

UPD3: After the analysis, it was determined that this problem affected a small number of participants. There are no submissions that get AC with the correct interactor and erroneously received a non-AC verdict earlier. Therefore, the following decision was made:

If your solution worked with the old interactor, but does not work with the correct one and your rating has decreased, then the round will be unrated for you.

UPD4: Congratulations to the winners!

Div.1:

1. Kevin114514

2. tourist

3. Radewoosh

4. turmax

5. heuristica

Also, special thanks and congratulations to rainboy for being one and only one solving problem F in division 1!

Div.2:

1. Morisz10

2. Wxssim

3. Aurora14526

4. shardulisgapryongkim

5. igAC

Codeforces!

Proof_by_QED, chromate00, larush, Edeeva, and I would like to invite you to participate in Codeforces Round 1003 (Div. 4), starting on Feb/09/2025 17:35 (Moscow time). We have baked $$$8$$$ problems to be solved in $$$2$$$ hours and $$$15$$$ minutes. We hope the problems will be interesting, unique...and skibidi.

The format of the event will be identical to Div. 3 rounds:

• ICPC rules with a penalty of 10 minutes for an incorrect submission;
• 12-hour phase of open hacks after the end of the round (hacks do not give additional points)
• after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated
• by default, only "trusted" participants are shown in the results table (but the rating will be recalculated for all with initial ratings less than 1400 or you are an unrated participant/newcomer).

We urge participants whose rating is 1400+ not to register new accounts for the purpose of narcissism but to take part unofficially. Please do not spoil the contest for the official participants.

Only trusted participants of the fourth division will be included in the official standings table. This is a forced measure for combating unsporting behavior. To qualify as a trusted participant of the fourth division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them),
• do not have a point of 1400 or higher in the rating.

Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1400 (or you are a newcomer/unrated), you may choose to participate rated or unrated.

Large text, to get your attention for the following:

PLEASE NOTE the rule restricting AI use. If you are caught using AI in an unorthodox manner, either by us manually or detected automatically, YOUR ACCOUNT WILL BE TERMINATED. We will be actively scouring submissions and terminating rulebreakers.

Anyways, I would like to orz the following:

• Vladosiya for coordinating.

• Our growing family of testuwuers: [VIP] Dominater069, Error_Yuan, amoeba4, Intellegent, [VIP] LMeyling, temporary1, efishel, 18o3, -firefly-, __baozii__, monadtransformer, Sacharlemagne, Lilypad, kevlu8, Filikec, [VIP-] macaquedev, hashman, mathtsai, DivinePunishment, pianapolataa, reirugan, and poi.

• MikeMirzayanov for running this site for 15 years. 15 years ago, I was still eating crayons.

UPD: Editorial

UPD2: Regarding Skipped Submissions

Greetings Codeforces community!

We are excited to announce the Constructor Open Cup 2025, our annual online programming competition organized by Constructor University and JetBrains.

What is the Constructor Open Cup 2025?

Constructor Open Cup is an online contest organized by Constructor University and JetBrains, the global leading tool provider for developers, to promote interest in computer science, data science, software development, and software engineering.

Put your knowledge and skills to the test in this 4-hour competition and stand a chance to walk away with a scholarship for a bachelor's degree in Software, Data and Technology (BSc SDT) at Constructor University, Germany’s #1 private university*!

Constructor Open Cup timetable

January 27 – February 5, 2025 | Practice Round

Get familiar with the testing environment during this practice round.

February 6, 2025, at 2 PM (UTC) | Main Round

You will have 4 hours to complete a series of algorithmic programming tasks. Registration closes 1 hour before the start of the contest.

Prizes and Winner Announcement

The top candidates will receive exciting prizes, including:

• chance to get scholarships for the BSc SDT*
• exciting memorable gifts from Constructor University and JetBrains

*The winners who applied to the BSc SDT will receive an email to schedule the interview with Constructor University and JetBrains.

How can I participate?

• Register your details on the webpage.
• Finalize your registration at Codeforces using the link you receive in the confirmation email.
• If you have any further queries, please reach out to talent@constructor.university.

How can I prepare?

Prepare for the Constructor Open Cup 2025 with an online webinar on January 29 at 17:00 CET. Our expert will go over the problems from last year’s competition and share helpful tips.

• January 29 at 17:00 CET
• Link to join the webinar

Don’t forget to save the date!

Dear Codeforces,

I am honoured to share that the XI-th edition of the AGM International Programming Contest has officially begun!

AGM is addressed to High School students who compete in teams of up to 3 members, ICPC-style. The contest has 2 rounds:

1. The Qualification Round held online, on Saturday, the 1st of March 2025 between 14:00 and 19:00 GMT+2 (timeanddate)
2. The Final Round held onsite. The location, date and time will be announced soon.

Registrations are opened until Monday, the 24th of February 2025: https://forms.gle/zQ5dZKyTbYX1Xbpa7

The problem sets are entirely developed by current and former university students from the United Kingdom and Romania.

The top 10 teams of the Final Round will receive Diplomas. Additionally, the top 3 teams of the Final Round will receive cash prizes:

• I-st place: 1200 RON
• II-nd place: 900 RON
• III-rd place: 600 RON

In the meantime, please have a look over the last few years' problem sets here.

Here are some useful links:

• Website: https://agm-contest.com
• Facebook: @AGM.Contest
• Competition Rules: https://agm-contest.com/competition-rules
• E-mail address: contact@agm-contest.com

Finally, I am more than delighted to present our team: patrick.sava (the heart of the project), carabet.cosmin, Mihai22e, Stelutzu, munteanuvlad98, caesar2001, average_frog_enjoyer, popovicirobert, Alex18mai, ionan6ix, butasebi, Stefan_Radu, eman98, mihaicristian, yodoli27, cristb, venom1724, zarg169, alin_gb18, IacobTudor and me

We are looking forward to welcoming everyone!

Kind regards,

George

Ciao, Codeforces!

I am glad to offer you to participate in Codeforces Round 1002 (Div. 2), which starts at Feb/02/2025 17:35 (Moscow time).

The tasks were offered by me and Artem shfs. We hope you will find them interesting.

This round will be rated for all participants, with rating below 2100. Participants with higher rating can take part, but the round will be unrated for them.

You will be offered 5 tasks and 2 hours to solve them. The last task will be split in 2 parts.

I want to thank:

• shfs For help with creating tasks.
• Artyom123 for elegant coordination.
• our testers makrav, Anonymous_Noob, IzhitskiyTimofey, sadness, djm03178, ArSarapkin, max0000561, Vash_nick, AndreyPavlov, 127.0.0.1, Solove, nichke, dope, etian6795, umimel, daniel071292, _DuMoH4uK_, LittleTiredShpinatik_TwT, CodeCraftsPhoenix, marzipan, commitery, jj_d.
• MikeMirzayanov for Codeforces и Polygon.

We wish you good luch and rating as big as the bottle in the photo!

Point distribution: 500−1000−1500−2000−(1500−1500).

UPD: Editorial

Congratulations to the winners:

1. potato167
2. kotatsugame
3. Mangooste
4. Rubikun
5. maspy

Rated only:

1. RGB_ICPC8
2. Sanae
3. ydkm
4. jtrh
5. mj1000j

Hi, Codeforces!

Around this time, 15 years ago, I was deploying the first version of Codeforces on a server, registering my account, and writing the first post. 15 years have passed. Well, happy anniversary to us!

For me, this is the most exciting adventure — full of ups and downs, hard work, and moments of joy. What's amazing is that it was never a lonely journey. I've always had caring and reliable friends by my side! That includes the Codeforces team, coordinators and problem writers, our partners in various events, all community members, and, of course, our sponsors — steadfast supporters and helpers.

Look at what we've accomplished together! Here are some of the key metrics over the years. There seems to be plenty to celebrate!

On a day like this, of course, I want to share some good news. And we have some! We have fantastic news!

News #1. Our title sponsor, TON Foundation, has extended and expanded its support of our community. Honestly, I'm amazed by how many innovative projects are working on the TON blockchain. And their long-term and consistent support of the competitive programming community is a great gesture of trust. Thank you, TON!

News #2. In this context, I'd like to announce increased payouts for problem authors and coordinators. We all want to see new and exciting problems and regular rounds. Now, Div 1 + Div 2 round authors will receive 1150 USDT, and Div 2 round authors will receive 450 USDT. I hope this news will inspire the best of the best to organize rounds!

News #3. And that's not all! We're continuing to develop unique competitions in collaboration with TON Foundation. Very soon, you'll be able to participate in the first-ever competition on our platform for programming smart contracts on the TON network! I think this will be a fresh and exciting challenge for the competitive programming community.

News #4. From mid-February to March 9, we'll be hosting an entertaining Codeforces Blitz Cup 2025 with duels and live streams. It will be a small, friendly tournament. Its primary goal is to entertain — we want to try a different format and create a fun show from the community for the community. Sounds interesting?

We want to invite experienced participants from different communities and countries. Participants should be ready for some show elements—mini-interviews, helping with commentary, and participating with screen-sharing and webcams. If you're red (or have been red) and are interested in giving it a try, fill out the participant application form, and we'll consider your application!

That's all for now, I think. And now I'll go enjoy a piece of birthday cake.

Mike

P.S.
I've often been asked about repeating the crowdfunding campaign we last did five years ago. It's a great idea, and I'd love to do it again! Right now, there are some organizational and bureaucratic challenges to launching it properly. Let's see how they get resolved. Maybe we'll kick it off soon—or perhaps we'll wait for the next round binary date at 16 years!

Hi Codeforces!

As the Chinese New Year approaches, we are glad to invite you to our Codeforces Round Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2) which will be held on Jan/26/2025 17:35 (Moscow time). You will be presented with $$$8$$$ problems, one of which is divided into two subtasks, and $$$2.5$$$ hours to solve them. This round will be rated for all participants.

This round is the first Div. 1 + Div. 2 round on Codeforces with a four-digit round number, and it is also my first round. We hope you will enjoy this round.

Great thanks to:

• SSerxhs for helping me prepare most problems,
• Yakumo_Ran for providing some problems,
• TheScrasse for good coordination of this round,
• Alexdat2000 for translating all statements to Russian,
• jqdai0815, ugly2333, dXqwq, Sugar_fan, propane, LuCpp, triple__a, PinkieRabbit, fallleaves01, thenymphsofdelphi, N_z__, tarjen, tiger2005, golomb, Tobo, add10k, Kieray, meowcneil, huansir, interlude, Cai_Guang, fr200110217102, nanani, Retired_shstyle, Theresa_Apocalypse, wjy666, PaperCloud, Kepy, _Sherbiny, nnv-nick, EternalJourney, shendeliliang, Teatify, sabino1, larush, Kraska, MeIoN_is_UMP45, weebyes, Enderwitherzjdl for testing our round,
• MikeMirzayanov for the amazing Codeforces and Polygon platforms.

Good luck & Have fun!

upd1: The score distribution is as follows: $$$500 - 1000 - 1000 - 2000 - (1500 + 2500) - 3500 - 4000 - 4500$$$

A few words from our sponsor:

Hello, Codeforces!

We are Ethflow, a proprietary trading fund specializing in cryptocurrency trading, and we’re glad to host our first Codeforces round!

Participants will have a chance to win T-shirts:

• The top 50 ranked competitors.
• 50 random participants who solve at least 3 problems and rank below 50th place.

Our team includes Codeforces grandmasters, IOI/IMO medalists, and ICPC Finals competitors. At Ethflow, we value people and create an environment where you can focus on challenges you enjoy, exploring everything from infrastructure to analytics without toxic practices. To join our team, please fill out the form.

Good luck to all participants!

upd2: Editorial

Congratulations to the winners!

1. orzdevinwang
2. ksun48
3. tourist
4. squareOf105
5. potato167

Hello, Codeforces! We are Ethflow — proprietary trading fund, specializing in cryptocurrency trading. We are glad to host our first Codeforces round!

All participants will have a chance to win T-shirts (top 50 + 50 random participants who ranked below 50th place and solved at least 3 problems).

Many of our team members, such as VEGAnn, _Time_Lord_, welleyth, FLEA, vgzowski and others, are former Codeforces participants, including our CEO, altruist and CTO, SoMuchDrama. Now, some of them were involved in four different roles over time: first as participants, then as teachers and problem setters, and now as sponsors. Currently, our team includes 7 IOI medalists, 1 IMO medalist, as well as ICPC Finals participants from both the previous and current years.

Ethflow is not just yet another HFT company. The core of our culture is putting people first, we create an environment and atmosphere where you can choose the problem you enjoy and excel at, with the freedom to explore everything from infrastructure to analytics problems. We do not tolerate toxic work culture or 60h per week mandatory working. We do believe in a decentralized finance future and work with cutting edge blockchain technology. Fortunately for the participants, we didn’t create the problems ourselves this time (maybe next time)

WARNING! If you want to work with us – please don’t. We want you to focus on real world problems, creating economic value and something useful for society, as all people know proprietary trading is not such a thing (you can ask your friends from big tech companies, they will say so). In the AI era with AGI on the horizon by 2030, there will be more awesome applications and areas where you can bring something valuable and apply your mind. There is no way back.

If nothing from above helped, please welcome — link to the form.

Hello Codeforces, and the legends of across $$$999$$$ and more rounds!

wuhudsm, Yugandhar_Master, and I are beyond excited to invite you to Codeforces Round 1000 (Div. 2) at Jan/22/2025 15:05 (Moscow time). Please note the unusual time of the round ($$$\color{red}{2.5}$$$ hours before the usual time)!

The contest contains $$$6$$$ carefully crafted tasks, one of them divided into two subtasks, to be solved in $$$2$$$ hours. You will solve tasks themed around Little John and his shenanigans aimed towards getting his own dream home (featuring, probably, galvanized square steel).

This round could not exist without the thankful help of these so many people:

• FairyWinx for rejecting more tasks than are used in the final problemset, coordinating the round and translating the problems;
• rewhile for some very important "technical assistance";
• the testers of Codeforces Round 960 (Div. 2), who had tested a non-empty subset of the problemset;
• antontrygubO_o for nutella testing;
• Dominater069, _istil, Error_Yuan, Monogon, awesomeguy856 for red testing;
• defnotmee, Proof_by_QED, -firefly-, Intellegent, efishel, priyanshu.p, amoeba4, evenvalue, cry, LMeyling, temporary1 for yellow testing;
• Wxssim, HusseinFarhat, Mukundan314, turska, rewhile, redheadphone for purple testing;
• Dragokj03, VladiG, b00s, SirPh, mathtsai, hashman, redpanda, larush, satyam343, antares2262, ismailfateen for blue testing;
• Valenz, shuniko for cyan testing;
• Dominater069 for identifying as green;
• tibinyte2006 for legendary-fake-lying-face grey testing;
• a few people who were invited to test but forgot/didn't have time for it;
• a few people who tested $$$\mathcal{O}(1)$$$ tasks individually but not the entire problemset;
• MikeMirzayanov for great platforms Codeforces and Polygon;
• and last but not least, You for participating! Thank you for writing legends in real-time for across $$$999$$$ and more rounds!

The score distribution is as follows.

Before finishing the announcement, I would like to spoil you a little of how the round's story ends.

Little John worked hard, honest and diligent for years, and finally got a home of his dream.

In that sense, I want You to be like Little John in this round.

Hard, honest and diligent will give you the rewards you deserve.

Anyways, that's all for the announcement; Good luck, and have fun!

UPD1: The score distribution has been announced.

UPD2: The editorial is posted here. Also we have good news that I will post as a separate report blog soon...

UPD3: Congratulations to the winners!

All participants:

1. sunjia (oops, the user is gone now)
2. Golovanov399
3. maspy
4. jiangbowen
5. A_G
6. fnoihzhyan

Rated only:

1. sunjia (oops, the user is gone now)
2. fnoihzhyan
3. RGB_ICPC9
4. wangzirui123
5. Network_Error
6. BSpioneer

UPD4: Anti-LLM Evaluation Report is published — the first of its kind for Div.2! Please kindly take a look if you have some free time or are just interested.