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

int k;
ll n = 1;
ld ans = 0, ans1 = -1;

int main() {
  cin >> k;
  while (ans != ans1) {
    ans1 = ans;
    ans += (ld)1 / (n * (n + k)); 
    n++;
  }
  cout << fixed << setprecision(15) << ans << endl;
  return 0;
}