import random

n = int(input())
k = int(input())

num = 800000
random.seed()
win = 0
for i in range(num):
    taro, jiro = 0, 0
    for j in range(n):
        jiro += random.randint(1, 6)
    for l in range(k):
        taro += random.randint(4, 6)
    for m in range(n-k):
        taro += random.randint(1, 6)
    if taro > jiro:
        win += 1
        
print(win/num)