#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1);
int main(){
  cout << fixed << setprecision(10);
  int k;
  cin >> k;
  if (k == 0){
    cout << PI * PI / 6 << endl;
  } else {
    double ans = 0;
    for (int i = 1; i <= k; i++){
      ans += (double) 1 / i;
    }
    ans /= k;
    cout << ans << endl;
  }
}