1111111

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
int n;
cin >> n;

double sum = 0.0;
for (int i = 1; i <= n; i++){
    double denominator = i * (i + 1) / 2.0;
    sum += 1.0 / denominator;
}
cout << fixed << setprecision(2) << sum << endl;
return 0;

}