dp1 = [0] * 61
dp2 = [0] * 61
dp1[0] = dp2[0] = 1
n = int(input())
k = int(input())
for _ in range(n):
    for i in range(54, -1, -1):
        for j in range(1, 7):
            dp1[i+j] += dp1[i]
        dp1[i] = 0
for _ in range(k):
    for i in range(54, -1, -1):
        for j in range(4, 7):
            dp2[i+j] += dp2[i] * 2
        dp2[i] = 0
for _ in range(n-k):
    for i in range(54, -1, -1):
        for j in range(1, 7):
            dp2[i+j] += dp2[i]
        dp2[i] = 0
for i in range(59, -1, -1):
    dp2[i] += dp2[i+1]
print(sum(dp1[i] * dp2[i+1] for i in range(60)) / 6 ** (2 * n))