#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>
#include <iomanip>
#include <random>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

default_random_engine gen;
uniform_int_distribution<int> futu(1, 6);
uniform_int_distribution<int> ikasama(4, 6);

int solve(int N, int K) {

  int taro = 0, jiro = 0;
  rep(i, N-K) {
    taro += futu(gen);
    jiro += futu(gen);
  }
  rep(i, K) {
    taro += ikasama(gen);
    jiro += futu(gen);
  }
  return taro > jiro;
}

int main() {

  int N, K; cin >> N >> K;

  ll ans = 0;
  rep(_, 1000000) {
    ans += solve(N, K);
  }

  cout << setprecision(5) << (double)ans / 1000000 << endl;

  return 0;
}