Hello all, This is a problem from the recent contest Codeforces Round #643 Div 2 named Game with Array (Problem D).

First claim of the editorial is that the answer is "NO" if S<2*N. I find it difficult to reach this conclusion during the contest.

As I can see that a lot of people were able to solve this problem during the contest, so I would like to hear your exact thought process/intuition/reasoning which you used during the contest. It would be great if you explain in detail.

Thank you.