Hello, dear Codeforces community!

I'm glad to present you the next Codeforces Round #121. The contest is brought to you by Ivan Smirnov (ifsmirnov) and Aleksandr Timin (AlTimin), the students of Moscow Institute of Physics and Technology. In our first round we will offer you a good time in Berland: you will hold a demonstration, prevent the demonstration, deal with the most important problems of Berland (with both of them!) and much more.

We thank Gerald a lot for the invaluable help he gave as during the contest preparation. He is also the author of one task in the contest. We also thank Delinur for the English version of statements, Aksenov239 for proofreading the statements and MikeMirzayanov for an opportunity to hold a contest on this wonderful site.

As usual, the contest will be held in both divisions and the problemsets will overlap. The scoring will be published later.

We wish you good luck and hope that you enjoy the contest!

UPD1: The scoring is classic in both divisions — 500-1000-1500-2000-2500.

UPD2: The contest authors apologize to the contesters for a possibility of misunderstanding of problem B div 1 (D div 2). The statement was fixed soon enough and the incorrect understanding of the problem didn't pass pretests, so the round is rated.

The contest is over; the editorial is here. I've mis-estimated the complexity of the problems — but how could I possibly guess who will arrive and finish everything in 40 minutes :-) Congratulations to the winners — the slowest and the most relaxed of them took under an hour to solve all the problems.

Today's round features Roco — a little-known esoteric language with a special approach to loops and subroutines. The programs written in it look a bit bulky, especially when compared to Befunge, but this is compensated by their relative simplicity and readability. Here is a program which calculates the sum of two given numbers:

iin [0]
iin [1]
add [2] [1] [0]
iout [2]
ac

There is little information about this language on the web — the only two sources known to me are the author's site and Progopedia article with commented sample programs.

There is also exactly one interpreter for Roco, written by its author. To run it, one has to have C++ installed (the author uses g++, and so do we), compile the interpreter source code into an executable file and run programs using command "roco program.roco". You can download the interpreter here.

Hi!

There are a lot of contests and trainings on Codeforces now. And it's difficult to find a tutorial or announcement for a specific contest.

And now you have an opportunity to attach materials (Codeforces blogs or external URLs) to any contest. You can click on the paperclip below blog's title and fill the popup form to attach blog entry to the contest. Or you can attach any URL in the contest's sidebar frame. There you can see resources that are already attached to the contest. Visibility of material depends on user's locale and current phase of the contest. For example you can't view statements before contest start.

The access to manage (add or delete) resources of the contest have administrators, contest managers and all "red" users.

The contests starts at 12.00 MSK.

There are some links where you can get some information about the conduct of the contest.

• official site, see results and video coverage here
• alternative standings
• Petr's Mitrichev blog

Have fun watching the finals!

Kostroma and I are problemsetters of Codeforces Round #120. It's first our contest and we hope you (and we too) will like it.

It's round for second division, but we think that everyone will find interesting problem for him.

Thanks for the help STAJIKER, HeroShadow, victor_kamashev, Abra, ifsmirnov, Aksenov239 and Gerald.
Thanks MikeMirzayanov for CodeForces platform and Delinur for English statements.

Good luck!

UPD: As usual, problems will cost 500-1000-1500-2000-2500 points.
UPD2: Problems are sorted according to expected difficulty.
UPD3: There was our mistake. The editorial was available for few minutes. If you see it, please not discuss problems and solutions. Now it is hided. In any case the round will be held. Decision, will contest rated or not will be made after contest. We are sorry for that.
UPD4: It's now known that only three participants from Div.2 have seen page with editorial while it was published (and 8 people in total). We'll not say any names, but we ask this people to not say anybody anything about the problem and to not use any post materials, if you have them. Thanks in advance.
UPD5: Please, don't panic. While your solution is in queue, you may solve other problems.
UPD6: Due to technical issues round is considered unrated. This problem and incident with editorial are strong enough reason for this decision. You may send your solutions to contest. They will be judged. We hope, that these technical problems will not spoil your impression about this round. Our sincere apologies. UPD7: Contest is over. Editorial is published. We hope, you like problems, prepared by us. We apologize again.
P.S: Excuse me, I don't know, when solution will be judged.

On the second day of staying in the Polish capital we went for a walk in the city centre. It was cold, windy and a little rainy, so those of us who hadn't taken any warm clothes to Poland, had to buy hats, scarves and jumpers with Polish national symbols in souvenir shops. We were very impressed by the Old Town (Stare Miasto) that was destroyed in the World War II but then rebuilt. Actually, that's what comes to my mind when I imagine a historical centre of a European city: narrow sett-paved streats, clock towers with high spines, tiled roofs...

This entry begins a small account of the journey Saratov State University delegation has left for the World Finals of the ACM ICPC 2012. The destination is Warsaw, where the World Finals take place this year. The delegation members are:

• Maxim Ivanov (e-maxx), Artem Rakhov (RAD), Nickolay Kuznetsov (NALP) — the Saratov SU 2 team;
• Michail Mirzayanov, the coach, with his wife Katherine and his daughter Tanya;
• Antonina Fedorova and Tatiana Semenova, our administrators;
• and finally, me (Nerevar), as the second coach.

That is the team’s second and last journey to the finals (last year they brought silver medals from Orlando). And for me this is the first journey to the Finals not as a participant (I participated in 2009 and 2010, and was a success too).

Hello everyone,

We are glad to invite you to participate in today’s round.

Problems have been prepared by poopi, Mohammad_JRS, Gerald and me. The hero of our contest is called “PMP”. It is actually the base of our team name through the last five years. The stories are metaphoric, but they have some traces in truth.

This Codeforces round, is the last round before the incoming ICPC world final. Our best wishes for all participants of that contest, too.

I want to specially thank Gerald for his helps and advices in problem preparation, Delinur for translation of statements into Russian and MikeMirzayanov for this great system.

And we have a modified version of Burunduk1 ’s advice: “to make the round even more interesting for us, read the statements of ALL problems.” :)

We hope you enjoy the problems and have high ratings.

Update: Contest is over. Thanks to everyone for taking part and congratulations to the winners of both divisions, specially peter50216 for being the only who solved all the problems of division 1! :)

Update: Editorial

Good Morning, Codeforces!

Analyzing the task C (Div1), E (div2) I came to the conclusion that the author's solution is wrong, so I bring to you all a huge apology.

However it turned out all pretests were correct and there are only a few number of incorrect hacks (only 3). After discussing the situation with MikeMirzayanov we made ​​this decision:

• Problem E almost do not effect on contest results for Div2 participants (there are only a few number of submits and no hacks), so the contest will be rated for Div2 participants.

• The contest will be rated for Div1 participants, only if this problem have right and fast solution. I wasted all todays night (or morning) finding this solution. Therefore I propose to solve this problem by the community (if it's possible). If during the day, i.e. 24 hours after publishing this post, one cannot find solution, Div1 competition will be considered unrated.

Once again I bring you my apologies for this mistake. I hope that we will be able to master this problem together. Feel free to write all your ideas in this post, even some wrong idea may hint at the right solution. We would be very grateful to everyone who will take part in solving of that problem.

Note that this problem appeared in problemset. All tests are correct and you may try to solve it.

UPD: 24 hours have passed. Unfortunately, no one has written the correct solution, or close to it. Div1 round is declared unrated. Many thanks to all those who put their efforts and tried to solve this problem.

Best regards, Gerald Agapov.

Hello everybody! There is less than 3 hours before my second codeforces round, in which I participating as author. (The first one was — Codeforces Beta Round 56.) It will be llok like the previous one. (That was not bad, I wish. :-)!) I wish, you like today's contest.

I'm the author of this round, except one problem, which was proposed by Gerald.

In preparing this round was participating : Gerald (He always makes problems better.), cerealguy (Who helps in preparing, i think, the hardest problem of this round. He had solved the first version of round — and think, that it's easy.), Delinur (Who translate the problems). And also it was done with help of "Polygon" and "Codeforces".

I wish, you luck in this contest and to have high rating.

Problem scores will be as always. I wish, that problems are sorted well.

UPD: I'm very bad man, and have written wrong solution in problem "C". Problem under investigation.