#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

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

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

    const int T = 1000000;
    int win = 0;
    for(int i=0; i<T; ++i){
        int a = 0;
        for(int j=0; j<n; ++j)
            a += xor128() % 6 + 1;

        int b = 0;
        for(int j=0; j<n-k; ++j)
            b += xor128() % 6 + 1;
        for(int j=0; j<k; ++j)
            b += xor128() % 3 + 4;

        if(a > b)
            ++ win;
    }

    double ret = win / (double) T;
    cout.setf(ios_base::fixed, ios_base::floatfield);
    cout << setprecision(10) << ret << endl;

    return 0;
}