#include <iostream>
#include <sstream>
#include <vector>
#include <array>
#include <string>
#include <algorithm>
#include <map>
#include <cmath>
#include <random>

using namespace std;

#define REP(i,first,last) for (int i=first;i<last;++i)
#define MAX(x,y) (x > y ? x : y)
#define MIN(x,y) (x < y ? x : y)

int N, K;
int trial = 9000000;

int main(){
  cin >> N >> K;
  int taro_win = 0;

  REP(i,0,trial) {
    int taro_result = 0;
    int jiro_result = 0;

    REP(i,0,N){
      if (i < K) {
        taro_result += rand() % 3 + 4;
      } else {
        taro_result += rand() % 6 + 1;
        jiro_result += rand() % 6 + 1;
      }
    } 
    if (taro_result > jiro_result) ++taro_win;
  }
  printf("%.5f\n", (double)taro_win / trial);
}