#include <bits/stdc++.h>

using namespace std;

const int TRY = 10000000;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    srand((unsigned int)time(NULL));
    int n, k;
    cin >> n >> k;
    int cnt = 0;
    for (int i = 0; i < TRY; i++) {
        int taro = 0, jiro = 0;
        for (int j = 0; j < n; j++) jiro += rand() % 6 + 1;
        for (int j = 0; j < n - k; j++) taro += rand() % 6 + 1;
        for (int j = 0; j < k; j++) taro += rand() % 3 + 4;
        if (taro > jiro) cnt += 1;
    }
    cout << cnt * 1.0 / TRY << endl;
    return 0;
}