Dumbear likes to play table tennis with his daughter – Quan. But Dumbear found that Quan played table tennis better and better recently, Dumbear wondered that Quan would defeat him someday. So he wants to know if he will win in the next match.
To simplify the problem, you can assume that the probability of Dumbear’s winning in each match is a constant number P (But Dumbear and you don’t know the number exactly). Of course 0 ≤ P ≤ 1. Dumbear had already taken N matches with Quan. And he won for M matches. He wants to know the expected probability of his winning for the next match. But Dumbear is very dumb, so he wants you to help him.