// No.58 イカサマなサイコロ
#include <iostream>
#include <random>
#include <iomanip>
using namespace std;

int main() {
    int N, K;
    cin >> N >> K;
    int tot = 0, win = 0;
    for (int iter = 0; iter < 1000000; ++iter) {
        int a = 0, b = 0;
        for (int i = 0; i < N; ++i) a += rand() % 6 + 1;
        for (int i = 0; i < K; ++i) b += rand() % 3 + 4;
        for (int i = 0; i < N - K; ++i) b += rand() % 6 + 1;
        if (b > a) ++win;
        ++tot;
    }

    cout << fixed << setprecision(10) << (double)win / tot << endl;
}