from random import random

def my_randint(x,y):
    width = y - x + 1
    res = int(width * random()) + x - 1
    return res

N = int(input())
K = int(input())
trial = 100000

taro_win = 0

for _ in range(trial):
    taro_val = 0
    jiro_val = 0

    for i in range(N):
        if i < K:
            taro_val += my_randint(4,6)
        else:
            taro_val += my_randint(1,6)

    for i in range(N):
        jiro_val += my_randint(1,6)

    if taro_val > jiro_val:
        taro_win += 1

print(taro_win / trial)