#include <iostream>
#include <iomanip>
#include <vector>
using namespace std;
int main(){
	cout << fixed << setprecision(5);
	int N;
	cin >> N;
	int K;
	cin >> K;
	vector<vector<double>> dp(N + 1, vector<double>(N * 6 + 1, 0));
	dp[0][0] = 1;
	for (int i = 0; i < N; i++){
		for (int j = 0; j <= i * 6; j++){
			for (int k = 1; k <= 6; k++){
				dp[i + 1][j + k] += dp[i][j] / 6;
			}
		}
	}
	vector<vector<double>> dp2(N + 1, vector<double>(N * 6 + 1, 0));
	dp2[0][0] = 1;
	for (int i = 0; i < K; i++){
		for (int j = 0; j <= i * 6; j++){
			for (int k = 4; k <= 6; k++){
				dp2[i + 1][j + k] += dp2[i][j] / 3;
			}
		}
	}
	for (int i = K; i < N; i++){
		for (int j = 0; j <= i * 6; j++){
			for (int k = 1; k <= 6; k++){
				dp2[i + 1][j + k] += dp2[i][j] / 6;
			}
		}
	}
	double ans = 0;
	for (int i = 0; i <= N * 6; i++){
		for (int j = i + 1; j <= N * 6; j++){
			ans += dp[N][i] * dp2[N][j];
		}
	}
	cout << ans << endl;
}