#include <iostream>
#include <random>
#include <chrono>
using namespace std;

int bitcount(int a){
	int r = 0;
	while(a){
		r++;
		a -= a & -a;
	}
	return r;
}

int main(){
	int n, k;
	cin >> n >> k;
	random_device rnd;
	mt19937 mt(rnd());
	uniform_int_distribution<> rand16(1, 6), rand46(4, 6), randn(0, (1 << n) - 1);
	auto start = chrono::system_clock::now();
	int all = 0, win = 0;
	while(chrono::duration_cast<chrono::milliseconds>(chrono::system_clock::now() - start).count() < 4950){
		int puni = 0, muni = 0;
		int a = randn(mt);
		while(bitcount(a) != k) a = randn(mt);
		for(int i = 0; i < n; i++) puni += ((a >> i) & 1) ? rand46(mt) : rand16(mt);
		for(int i = 0; i < n; i++) muni += rand16(mt);
		all++;
		if(muni < puni) win++;
	}
	cout << 1. * win / all << endl;
}