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

static const int INF = 1000000;

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

	int A = 0, B = 0;
	while (B <= INF)
	{
		int a = 0, b =0;
		for (int i = 0; i < N; ++i)
			b += rand() % 6 + 1;
		for (int i = 0; i < K; ++i)
			a += rand() % 3 + 4;
		for (int i = 0; i < N - K; ++i)
			a += rand() % 6 + 1;

		if (a > b)
			++A;
		++B;
	}

	cout << (double)A / (double)B << endl;

	return 0;
}