#include <bits/stdc++.h>

int main() {

  int N, K;
  int win = 0;
  int times;
  int a, b;

  std::cin >> N >> K;

  times = 10000000;
  for(int i = 0; i < times; ++i) {
    a = 0;
    b = 0;
    for(int j = 0; j < N; ++j) {
      a += rand() % 6;
    }
    for(int j = 0; j < N-K; ++j) {
      b += rand() % 6;
    }
    for(int j = 0; j < K; ++j) {
      b += rand() % 3 + 3;
    }
    if( b > a ) {
      win += 1;
    }
  }

  std::cout << (double)win/times << std::endl;
  
  return 0;
}