N = int(input())
K = int(input())
D = [[1, 2, 3, 4, 5, 6], [4, 5, 6, 4, 5, 6]]

pre0 = [0] * 61
pre0[0] = 1
for i in range(N):
    dp0 = [0] * 61
    for j in range(61):
        for k in range(6):
            if D[0][k] + j > 60:
                continue
            dp0[D[0][k] + j] += pre0[j]
    dp0, pre0 = pre0, dp0
    
pre1 = [0] * 61
pre1[0] = 1
for i in range(N):
    dp1 = [0] * 61
    for j in range(61):
        for k in range(6):
            nex = D[int(i <= K-1)][k] + j
            if nex > 60:
                continue
            dp1[nex] += pre1[j]
    dp1, pre1 = pre1, dp1
    
ans = 0
for i in range(61):
    for j in range(i):
        ans += pre1[i] * pre0[j]
print(ans/(6**(2 * N)))