#include <iostream>
#include <vector>
using namespace std;

int main(void){
  int K;  cin >> K;
  vector<double> v(K, 0.0);
  v[K-1] = 1.0;
  for(int i = K-2; i >= 0; i--){
    double t = 0.0;
    for(int j = 1; j <= 6; j++){
      if(i + j >= K) continue;
      t += (v[i+j] / 6.0);
    }
    t += 1.0;
    v[i] = t;
  }
  cout << v[0] << endl;
  return 0;
}