#include <iostream>

using namespace std;

const int MAXN = 10;

int N, K;
double dp1[MAXN + 1][MAXN * 6 + 1];
double dp2[MAXN + 1][MAXN * 6 + 1];
double p1[MAXN * 6 + 1];

int main() {
	cin >> N >> K;
	dp1[0][0] = 1.0;
	for (int i = 0; i < N; i++) {
		for (int j = 1; j <= 6; j++) {
			for (int k = 0; k <= 6 * i; k++) {
				dp1[i + 1][k + j] += dp1[i][k] / 6.0;
			}
		}
	}
	for (int i = 0; i <= 6 * (N - K); i++) {
		dp2[N - K][i] = dp1[N - K][i];
	}
	for (int i = N - K; i < N; i++) {
		for (int j = 4; j <= 6; j++) {
			for (int k = 0; k <= 6 * i; k++) {
				dp2[i + 1][k + j] += dp2[i][k] / 3.0;
			}
		}
	}
	for (int i = N; i <= 6 * N; i++) {
		p1[i] = p1[i - 1] + dp1[N][i];
	}
	double win = 0.0;
	for (int i = N; i <= 6 * N; i++) {
		win += dp2[N][i] * p1[i - 1];
	}
	cout << win << endl;
	return 0;
}