#include <bits/stdc++.h>
using namespace std;

int main(void) {
	mt19937 mt{random_device{}()};
	uniform_int_distribution<int> d1(1, 6), d2(4, 6);
	
	int N, K;
	cin >> N >> K;
	
	int cnt = 0;
	for(int _ = 0; _ < 5000000; ++_) {
		int taro = 0, jiro = 0;
		for(int i = 0; i < N - K; ++i) taro += d1(mt);
		for(int i = 0; i < K; ++i) taro += d2(mt);
		for(int i = 0; i < N; ++i) jiro += d1(mt);
		
		if(jiro < taro) ++cnt;
	}
	
	cout << cnt / 5000000.0 << "\n";
	return 0;
}