#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int main() {
	int dice1[6] = {1, 2, 3, 4, 5, 6};
	int dice2[6] = {4, 4, 5, 5, 6, 6};
	int n, k;
	cin >> n >> k;
	int normals = n - k;

	vector< vector<int> > dp1(n + 1, vector<int>(n * 6 + 1 + 6, 0)), dp2;
	dp2 = dp1;
	for (int i = 0; i < 6; i++) {
		dp1[1][dice1[i]] = 1;
		int next2 = normals > 0 ? dice1[i] : dice2[i];
		dp2[1][next2] += 1;
	}

	for (int i = 2; i <= n; i++) {
		for (int j = 1; j <= 6 * n; j++) {
			if (dp1[i - 1][j] > 0) {
				for (int k = 0; k < 6; k++) {
					int next1 = dice1[k];
					dp1[i][j + next1] += dp1[i - 1][j];
				}
			}
			if (dp2[i - 1][j] > 0) {
				for (int k = 0; k < 6; k++) {
					int next2 = i <= normals ? dice1[k] : dice2[k];
					dp2[i][j + next2] += dp2[i - 1][j];
				}
			}
		}
	}

	vector<long long> sum(n * 6 + 1, 0);
	for (int i = 1; i <= n * 6; i++) {
		sum[i] = sum[i - 1] + dp1[n][i];
	}

	long long win = 0;
	for (int i = 0; i <= n * 6; i++) {
		if (dp2[n][i] > 0) {
			win += dp2[n][i] * sum[i - 1];
		}
		// printf("%2d %10d %10d %10lld\n", i, dp1[n][i], dp2[n][i], win);
	}
	double ans = 1.0 * win / sum[n * 6] / sum[n * 6];

	printf("%.6f\n", ans);
	return 0;
}