Problem A: Answer is floor(N*M*0.5). Since there is N*M cells on the board and each domino covers exactly two of them we cannot place more for sure. Now let's show how to place exactly this number of dominoes. If N is even, then place M rows of N/2 dominoes and cover the whole board. Else N is odd, so cover N-1 row of the board as shown above and put floor(M/2) dominoes to the last row. In the worst case (N and M are odd) one cell remains uncovered.
I am happy to tell you that Codeforces will soon free you from reading those endless "Please, give me test #??" in the comments. Now you can click on a link with the submission-id on the status page and it will show not only the original solution texts, but also the tests on which testing was performed (the judging system report). It will not contain the full inputs/outputs/answers if they are too large – you will have to wait for now and enjoy their prefixes. As soon as we understand that there're no bugs in the implementation, we will open all the previous contests to view the tests.
However, that is only the first step; later you will be able to download contest problem archives that will contain full texts (or their generators) as well as the authors' solutions and other materials.
Of course we do not want Codeforces problems to be copied from one "online judge" to another one. You’ve got to understand that Codeforces puts huge effort into preparing tasks and organizing contests. That's why we limit the material usage to make using our problems on websites or in other automatic testing systems impossible. On the other hand, we will be glad if the contest materials will be useful for individual training or for some assemblies, training sessions etc. with the onsite participants. Read the license text carefully as we want some Codeforces data to be published near (or inside) the problem tasks.
At the moment it is version 0.1 of the license, we will perhaps change a lot in it, but I guess the idea will undergo no changes.
Codeforces materials usage license (v. 0.1)
One more codeforces format round takes place this evening. I'm the author of the contest problems. Artem Rakhov and Maria Belova helped me to prepare the problems. Great thanks to them and all codeforces "fighters"!
I wish you good luck and funny hacks!
P.S: This round won't be rated. So your ratings won't change. That's because of severe problems with codeforces server. Read here for explanation.
Soon many of you will have your examinations, and someone even have it now. I wish you excellent marks and many easy exams!
Artem Rakhov and Codeforces team
Let me say the customary phrase "The series of school online Olympiads have ended!"
The organization of all the Olympiads was supported by Yandex and ABBYY companies. Overall 6 competitions took place, three team Olympiads and three individual ones. It is now high time we looked at the results and found the Olympiad winners. The two nominations (team contests and individual contests) were ratified individually – in each of them the results of the participants’ best two of three performances. Here are the links to the total results in each nomination:
Overall about 750 participants from all over the world had been registered during the series. Of course, the majority of them were Russian participants. As we can see, about 180 teams took part in the team contests and more than 400 school students took part in the individual contests.
I invite everyone to take part in the last contest of the series of WCS olympiads for school students which is one of the regular Codeforces rounds at the same time. The start of the contest is on the 12th of December, at 11:00 MSK.
The competition rules are ACM-ICPC rules, the duration of the contest is 3 hours.
Like the previous school individual olympiads, the contest will be rated for all participants (both for school students and others). Rating will be calculated according to the merged result table.
The authors of the problems are me and Dmitry Matov again. Thanks to Gerald Agapov and Artem Rakhov for their help in preparing the problems and to Maria Belova for translating the problem statements.
Good luck everyone!
The author's problem analysis is posted. Now problems G and H are added to the tutorial, too.
Thanks to everyone who participated in WCS series for school students, officially and unofficially!
Greetings to everybody.
I would like to invite you to take part in the next Codeforces competition, which will be held on 5th of December at 11:00 MSK. This competition will be a part of WCS olympiads (click here for details) and usual Codeforces round at the same time.
The official rules of the competition are ACM-ICPC rules. The duration of the competition is 3 hours.
Those who don't participate in selection to WCS will be displayed as "out of competition" in the result table. But everybody will get rating for this competition according to the merged result table.
This time the authors of the problems are Natalia Bondarenko and I. Thanks to Edvard Davtyan for his help in preparing the contest and to Maria Belova for translating problem statements.
Don't forget to register in order to take part in the competition. Good luck at the contest!