#include <iostream>
#include <cmath>
using namespace std;
int main(){
	double sum, eps, next, A;
	int i=1;
	eps=0.001;
	A=-1/3.0;
	sum=A;
	while (abs(A)>eps){
		i=i+1;
		sum=sum+A;
		next=A*(-2)/(2*i+3);
		A=next;
	}
 	cout << "sum="<< sum << endl << "i=" << i << endl;
 	return 0;
}