N = int(input())
K = int(input())

dp0 = [[0 for j in range(100)] for i in range(N + 1)]
dp1 = [[0 for j in range(100)] for i in range(N + 1)]
dp0[0][0] = 1
dp1[0][0] = 1

for i in range(N):
	for j in range(90):
		for k in range(1, 7): dp0[i + 1][j + k] += dp0[i][j]
		if i < K:
			for k in range(4, 7): dp1[i + 1][j + k] += dp1[i][j] * 2
		else:
			for k in range(1, 7): dp1[i + 1][j + k] += dp1[i][j]

whole = (6 ** N) ** 2
win = 0

for i in range(100):
	for j in range(i + 1, 100):
		win += dp0[N][i] * dp1[N][j]

print(win / whole)