Score : 300 points
Snuke has a fair N-sided die that shows the integers from 1 to N with equal probability and a fair coin. He will play the following game with them:
You are given N and K. Find the probability that Snuke wins the game.
Input is given from Standard Input in the following format:
N K
Print the probability that Snuke wins the game. The output is considered correct when the absolute or relative error is at most 10^{-9}.
3 10
0.145833333333
Thus, the probability that Snuke wins is \frac{1}{48} + \frac{1}{24} + \frac{1}{12} = \frac{7}{48} \simeq 0.1458333333.
100000 5
0.999973749998