N = int(input())
K = int(input())
L = 6*N
# 二郎
dp = [[0.0]*(L+1) for _ in range(N+1)]
dp[0][0] = 1.0
for i in range(N):
    for j in range(L+1):
        for k in range(1, 7):
            if j+k > L:
                continue
            dp[i+1][j+k] += dp[i][j]/6
# 太郎
ep = [[0.0]*(L+1) for _ in range(N+1)]
ep[0][0] = 1.0
for i in range(N):
    for j in range(L+1):
        if i < K:
            for k in range(4, 7):
                if j+k > L:
                    continue
                ep[i+1][j+k] += ep[i][j]/3
        else:
            for k in range(1, 7):
                if j+k > L:
                    continue
                ep[i+1][j+k] += ep[i][j]/6

ans = 0
for i in range(L+1):
    tmp = sum([dp[N][j] for j in range(i)])
    tmp *= ep[N][i]
    ans += tmp
print(ans)