#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

int k;
ld ans = 0;

int main() {
  cin >> k;
  if (k == 0) ans = M_PI * M_PI / 6;
  else {
    for (int n = 1; n <= k; n++) {
      ans += (ld)1 / n; 
    }
    ans *= (ld)1 / k;
  }
  cout << fixed << setprecision(15) << ans << endl;
  return 0;
}