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

int N;
vector<double> m(5001, -1);

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

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