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

int main() {
	int k; cin >> k;
	cout << fixed << setprecision(15);
	if (k == 0) {
		long double PI = 3.1415926535;
		cout << PI * PI / 6.0 << endl;
		return 0;
	}
	long double now = 0;
	for (int i = 1; i <= k; i++) {
		now += 1.0 / (long double)i;
	}
	now /= (long double)k;
	cout << now << endl;
	return 0;
}