#include <iostream>
#include <math.h>
using namespace std;

int main() {
	double E = 1e-1;
	double x = -1;
	double sum = 0.0;
	for(int i = 2; fabs(x) > E ; i++){
		sum += x;
		//cout << x << " " ;
		
		x *= (-1./i);
		 
	}
	cout << sum;
	return 0;
}