include "pch.h"

include

include<math.h>

using namespace std;

int main() {

//1
const double fenzi = 1.0;
int n;
cin >> n;
double sum = 0;
double fenmu = 1.0;
double flag = 1.0;

for (int i = 0; i < n; ++i)
{
	sum = sum + flag / fenmu;
	fenmu = fenmu + 2;
	flag = -flag;
	
}
cout << sum;

}