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

dice = [i for i in range(1,7)]
dice2 = [i for i in range(4,7)]

dp1 = [0]*(6*n+1)
dp2 = [0]*(6*n+1)
dp1[0] = 1
dp2[0] = 1

for i in range(n):
    ndp1 = [0]*(6*n+1)
    for j in range(6*n):
        for d in dice:
            if j+d <= 6*n:
                ndp1[j+d] += dp1[j]
    dp1 = ndp1

for i in range(n-k):
    ndp2 = [0]*(6*n+1)
    for j in range(6*n):
        for d in dice:
            if j+d <= 6*n:
                ndp2[j+d] += dp2[j]
    dp2 = ndp2

for i in range(k):
    ndp2 = [0]*(6*n+1)
    for j in range(6*n):
        for d in dice2:
            if j+d <= 6*n:
                ndp2[j+d] += dp2[j]*2
    dp2 = ndp2

p = sum(dp1)*sum(dp2)

count = 0
win = 0
for i in range(1,6*n+1):
    win += count*dp2[i]
    count += dp1[i]

print(win/p)