#include <iostream>
#include <cmath>
using namespace std;
int main() {
	float x, s, s1, n;
	s = 0;
	s1 = 0;
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		s = s + 1 / sqrt(i);
		s = s + s1;

	}
	cout << s;
	system("pause");
	return 0;


}