#include <iostream>
#include <cmath>
using namespace std;

const int MAX_N = 20;

int taro[MAX_N][MAX_N * 6], jiro[MAX_N][MAX_N * 6];

int main() {
    int n, k;
    cin >> n >> k;

    taro[0][0] = 1;
    jiro[0][0] = 1;
    for (auto i = 1; i <= n; i++) {
        for (auto sum = 1; sum <= n * 6; sum++) {
            for (auto d = 1; d <= 6; d++) {
                auto dice = (i <= k && d <= 3) ? d + 3 : d;
                if (sum - dice >= 0) {
                    taro[i][sum] += taro[i - 1][sum - dice];
                }
                if (sum - d >= 0) {
                    jiro[i][sum] += jiro[i - 1][sum - d];
                }
            }
        }
    }

    // 計算を軽くするため二郎君の分をsum以下の目の出し方とする
    for (auto sum = 1; sum <= n * 6; sum++) {
        jiro[n][sum] += jiro[n][sum - 1];
    }

    auto ans = 0.0;
    for (auto sum = 1; sum <= n * 6; sum++) {
        ans += (double)taro[n][sum] / pow(6, n) *
                    (double)jiro[n][sum - 1] / pow(6, n);
    }
    cout << ans << endl;

    return 0;
}