Now the winter SIS (Summer Informatics School) is taking place, and we, as part of the parallel A*+ with its teachers, have prepared a complete Codeforces Round.
The round will happen at Jan/05/2020 17:05 (Moscow time) and will last for 2 hours. There will be 6 problems in each division.
The tasks of the round were invented and prepared by ismagilov.code, devid, Volkov_Ivan, Jatana, karasek, polinarria, cookiedoth, AlesyaIvanova, doktorkrab, AliceG, D.Pavlenko, VFeafanov, LordVoidebug, forestryks, Ilistratov, seiko.iwasawa, DeadInsideOnTest993, Drozd_off under the guidance of teachers PavelKunyavskiy, VArtem, _meshanya_, Nebuchadnezzar.
Good luck everybody!
In problem E an error was made in the intended solution, an overflow of long type while calculating the answer. The first test, on which it happened, reached 4 participants (ainta aid Um_nik ecnerwala), among who two passed the pretests, and two others did not, though they should have. In automatic mode, it is not possible to test so that both answers are accepted, because the overflow changes the tests because of the way the requests are encrypted. So, we decided to test two pretest solutions on the old set of tests and the rest on the new one. As a result, three of the solutions passed the tests (congratulations!), and one received WA80 on the 17th answer inside the test, which is clearly not related to the overflow problems. Only the solution that takes into account the overflow problem can be used in upsolving.