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

int N;
map<int, double> mp;

double f(int n) {
  if (mp.count(n)) return mp[n];
  if (n == 0) return 0;
  double sum = 0;
  for (int i = 0; i < n; i++) sum += f(i) + f(n - i - 1);
  return mp[n] = sum / n + 1;
}

int main() {
  cin >> N;
  cout << fixed << setprecision(15) << f(N) << endl;
  return 0;
}