#include <iostream>
#include <random>
using namespace std;
random_device rd;
mt19937 mt(rd());

int n, k;
uniform_int_distribution<> rand1(1, 6);
uniform_int_distribution<> rand2(4, 6);

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

  int win = 0;
  for (int i = 0; i < 1000000; ++i) {
    int taro = 0, jiro = 0;
    for (int j = 0; j < n; ++j) jiro += rand1(mt);
    for (int j = 0; j < n - k; ++j) taro += rand1(mt);
    for (int j = 0; j < k; ++j) taro += rand2(mt);
    win += (taro > jiro);
  }
  cout << (double)win / 1000000.0 << '\n';
  return 0;
}