AtCoder Beginner Contest 105 is ongoing now, from August 11, 2018, 21:00 JST.

The writers are DEGwer, Drafear, square1001 and me.
The point values are: 100 — 200 — 300 — 400.

This contest will be unrated because of problems in English statement. At first, there is no English statement in problem A. 6 minutes after starting the contest, the English statement appeared, but it was too late. Sorry for inconvenience.

After the contest, let's discuss the problem.
Thank you for your participation.