#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;
  vector<int> taro_sai(N);
  vector<int> jiro_sai(N);

  REP(i,0,trial) {
    int result = 0;
    REP(i,0,N){
      if (i < K) {
        result += rand() % 3 + 4;
      } else {
        result += rand() % 6 + 1;
      }
    }
    taro_sai.push_back(result);
  }

  REP(i,0,trial) {
    int result = 0;
    REP(i,0,N){
      result += rand() % 6 + 1;
    }
    jiro_sai.push_back(result);
  }

  double count = 0.0;
  REP(i,0,trial){
    if (taro_sai[i] > jiro_sai[i]) ++count;
  }

  printf("%1.5f\n", count / trial);
}