#include <iostream>
using namespace std;

int n, k;

bool calc(void) {
  int taro = 0;
  for(int i = 0; i < k; ++i) taro += (rand() % 3 + 4);
  for(int i = 0; i < n - k; ++i) taro += (rand() % 6 + 1);
  int jiro = 0;
  for(int i = 0; i < n; ++i) jiro += (rand() % 6 + 1);
  return taro > jiro;
}

int main() {
  cin>>n>>k;
  double win = 0, test = 8000000;
  for(int i = 0; i < test; ++i) if(calc()) win++;
  cout<<(win/test)<<endl;
}