Help in a Combinatoric problem

Revision en1, by Virtual_Contestant, 2020-05-05 20:28:20

Can anyone please explain the solution for this problem? I have looked at multiple solutions and editorial but unable to understand from them. Thanks a lot. https://codeforces.net/problemset/problem/804/B

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en1 English Virtual_Contestant 2020-05-05 20:28:20 235 Initial revision (published)