import random

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

tes = 10**5
cnt = 0
for i in range(tes):
    taro = 0
    jiro = 0
    for j in range(n):
        if j < k:
            taro += random.randint(4, 6)
        else:
            taro += random.randint(1, 6)
        jiro += random.randint(1, 6)
    if taro > jiro:
        cnt += 1
res = cnt / tes

print(res)