#include <iostream>
#include <string>
#include <vector>
#include <set>
#include <cmath>
#include <stack>
#include <algorithm>
#include <iomanip>
#include <map>
#include <queue>
#include <functional>
#include <numeric>
#include <chrono>
using ll = long long;
using namespace std;

const ll MOD = 1e9 + 7;
#define REP(i, n) for (int(i) = 0; (i) < (n); ++(i))
// bool operator<(const pair<int, int> &a, const pair<int, int> &b)
// {
//     if (a.first == b.first)
//         return a.second < b.second;
//     return a.first < b.first;
// };

unsigned int xor128(void)
{
    static unsigned int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
    unsigned int t = (x ^ (x << 11));
    x = y;
    y = z;
    z = w;
    return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
unsigned int xor128rnd(unsigned int m)
{
    return xor128() % m;
}

int main(void)
{
    int N, K;
    cin >> N >> K;

    clock_t t = clock() + CLOCKS_PER_SEC * 2;

    int win = 0, total = 1;
    while (t >= clock())
    {
        int sum = 0;
        REP(i, N)
        sum += xor128rnd(6) + 1;
        REP(i, N - K)
        sum -= xor128rnd(6) + 1;
        REP(i, K)
        sum -= xor128rnd(3) + 4;
        if (sum < 0)
            win++;
        total++;
    }
    cout << fixed << setprecision(9) << 1.0 * win / total << endl;
    return 0;
}