#include<iostream>
using namespace std;

int main()
{
	cout.precision(15);
	double tolerance = 1e-5;
	int i=1;
	double term = 1+tolerance;
	double sum = 0;
	while (abs(term) > tolerance)
	{
		term = i / pow(-2.0, i-1);
		sum = sum + term;
		i = i + 1;
	}
	cout << " sum = " << sum << endl;
}