import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import numpy as np

N,K = map(int,read().split())

def update(dp,dice):
    newdp = np.zeros(61,np.int64)
    for x in dice:
        newdp[x:] += dp[:-x]
    return newdp

D1 = [1,2,3,4,5,6]
D2 = [4,5,6,4,5,6]
A = np.zeros(61,np.int64)
A[0] = 1
for _ in range(N):
    A = update(A, D1)
B = np.zeros(61,np.int64)
B[0] = 1
for _ in range(K):
    B = update(B, D2)
for _ in range(N-K):
    B = update(B, D1)

den = A.sum() * B.sum()
num = 0
for a in range(61):
    num += A[a] * B[a+1:].sum()

print(num / den)