n = int(input())
k = int(input())
c1 = [0] * (6 * n + 1)
c2 = [0] * (6 * n + 1)
from itertools import product
for p in product([1,2,3,4,5,6], repeat=n):
    c1[sum(p)] += 1
for p1 in product([1,2,3,4,5,6], repeat=n-k):
    for p2 in product([4,4,5,5,6,6], repeat=k):
        c2[sum(p1)+sum(p2)] += 1
for i in range(6 * n - 1, -1, -1):
    c2[i] += c2[i+1]

wincnt = sum(c1[i] * c2[i+1] for i in range(6 * n))
print(wincnt / 6 ** (2 * n))