# -*- coding: utf-8 -*-

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

max_sum = 6 * N

# Taro
# dp1[num_used][cur_sum] = num of such pattern
# 普通のサイコロ→イカサマサイコロの順で考える
dp1 = [[0] * (max_sum + 1) for i in range(N + 1)]

if N - K > 0:
    # 普通のサイコロがあるとき
    for j in range(1, 6 + 1):
        dp1[1][j] = 1
else:
    for j in range(4, 6 + 1):
        dp1[1][j] = 2

# 配るDP
for n in range(1, N - K):
    for s in range(1, max_sum + 1):
        for d in range(1, 6 + 1):
            if s + d <= max_sum:
                dp1[n + 1][s + d] += dp1[n][s]

for n in range(N - K, N):
    for s in range(1, max_sum + 1):
        for d in range(4, 6 + 1):
            if s + d <= max_sum:
                dp1[n + 1][s + d] += 2 * dp1[n][s]

# Jiro
dp2 = [[0] * (max_sum + 1) for i in range(N + 1)]
for j in range(1, 6 + 1):
    dp2[1][j] = 1

for n in range(1, N):
    for s in range(1, max_sum + 1):
        for d in range(1, 6 + 1):
            if s + d <= max_sum:
                dp2[n + 1][s + d] += dp2[n][s]

cumu2 = 0
ans = 0
for s in range(2, max_sum + 1):
    cumu2 += dp2[N][s-1]
    ans += dp1[N][s] * cumu2

for i in range(2 * N):
    ans /= 6

print(ans)