#include<bits/stdc++.h>
using namespace std;
#ifdef LOCAL_DEBUG
  #include "LOCAL_DEBUG.hpp"
#endif
#define int long long
const double eps = 1e-7;

signed main(){

  int k; cin >> k;

  double left = 0, right = 200;
  while(right - left > eps){
    double mid = (left + right) / 2;
    vector<double> dp(k+10, 0);
    dp[0] = 0;
    for(int i = 1; i <= k; i++){
      for(int j = 1; j <= 6; j++){
        if(i - j >= 0){
          dp[i] += 1.0 * (1 + dp[i - j]) / 6;
        }else{
          dp[i] += 1.0 * (1 + mid) / 6;
        }
      }
    }
    (dp[k] >= mid ? left : right) = mid;
  }
  printf("%.7f\n", right);

  return 0;
}