#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  if (n == 0) {
    cout << fixed << setprecision(15) << acos(-1) * acos(-1) / 6 << endl;
  }
  else {
    double ans = 0;
    rep(i, n) ans += 1.0 / (i + 1);
    cout << fixed << setprecision(15) << ans / n << endl;
  }
  return 0;
}