Problem Statement

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:

• Throw the die. The current score is the result of the die.
• As long as the score is between 1 and K-1 (inclusive), keep flipping the coin. The score is doubled each time the coin lands heads up, and the score becomes 0 if the coin lands tails up.
• The game ends when the score becomes 0 or becomes K or above. Snuke wins if the score is K or above, and loses if the score is 0.

You are given N and K. Find the probability that Snuke wins the game.

Input

Input is given from Standard Input in the following format:
N K

Output

Print the probability that Snuke wins the game. The output is considered correct when the absolute or relative error is at most 10^{-9}.

Constraints

• 1 ≤ N ≤ 10^5
• 1 ≤ K ≤ 10^5
• All values in input are integers.

Sample Input 1

3 10

Sample Output 1

0.145833333333

• If the die shows 1, Snuke needs to get four consecutive heads from four coin flips to obtain a score of 10 or above. The probability of this happening is $\frac{1}{3} \times (\frac{1}{2})^4 = \frac{1}{48}$.
• If the die shows 2, Snuke needs to get three consecutive heads from three coin flips to obtain a score of 10 or above. The probability of this happening is $\frac{1}{3} \times (\frac{1}{2})^3 = \frac{1}{24}$.
• If the die shows 3, Snuke needs to get two consecutive heads from two coin flips to obtain a score of 10 or above. The probability of this happening is $\frac{1}{3} \times (\frac{1}{2})^2 = \frac{1}{12}$.

Thus, the probability that Snuke wins is $\frac{1}{48} + \frac{1}{24} + \frac{1}{12} = \frac{7}{48} \simeq 0.1458333333$.

Sample Input 2

100000 5

Sample Output 2

0.999973749998

见题面 Input 部分

见题面 Output 部分