#include <bits/stdc++.h>
using namespace std;

unordered_map<int, double> m;

double f(int n) {
    if(m.count(n)) 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() {
    int N;
    cin>>N;
    cout << fixed << setprecision(15) << f(N) << endl;
}