# coding: utf-8
# Your code here!
import sys
read = sys.stdin.read
readline = sys.stdin.readline

n = int(readline())
k = int(readline())
M = 6*n+1

dp1 = [0]*M
dp1[0] = 1
for _ in range(n):
    for i in range(M-7,-1,-1):
        for j in range(1,7):
            dp1[i+j] += dp1[i]
        dp1[i] = 0
    
dp2 = [0]*M
dp2[0] = 1
for _ in range(n-k):
    for i in range(M-7,-1,-1):
        for j in range(1,7):
            dp2[i+j] += dp2[i]
        dp2[i] = 0
for _ in range(k):
    for i in range(M-7,-1,-1):
        for j in [4,5,6,4,5,6]:
            dp2[i+j] += dp2[i]
        dp2[i] = 0

ans = 0
for i in range(M):
    for j in range(i):
        ans += dp2[i]*dp1[j]

#print(dp1,dp2,sum(dp1),sum(dp2))

print(ans/pow(36,n))