#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int K;
  cin >> K;
  double res = 0;
  for (double i = 1;; i++) {
    auto prev = res;
    res += static_cast<double>(1) / (i * (i + K));
    if (prev == res) break;
  }
  cout << fixed << setprecision(10) << res << '\n';
  return 0;
}