n = int(raw_input())
m = int(raw_input())
x = [[0 for _ in range(n*6+1)] for _ in range(n+1)]
x[0][0] = 1
for i in range(n):
    for j in range((n-1)*6+1):
        if i < m:
            for k in range(4,7):
                x[i+1][j+k] += x[i][j] * 2
        else:
            for k in range(1,7):
                x[i+1][j+k] += x[i][j]
y = [[0 for _ in range(n*6+1)] for _ in range(n+1)]
y[0][0] = 1
for i in range(n):
    for j in range((n-1)*6+1):
        for k in range(1,7):
            y[i+1][j+k] += y[i][j]
s = 0
for i in range(n*6+1):
    s += y[n][i] * sum(x[n][i+1:])
print float(s) / float(6**(2*n))