#include<iostream>
using namespace std;

int main()
{
	int n, m;
	double suma = 0;

	do
	{
		cout << "Unesite m: ";
		cin >> m;
	} while (m < 0);
	do
	{
		cout << "unesite n: ";
		cin >> n;
	} while (n < 0);

	for (int i = 1; i <= m; i++)
	{
		if (i % 2 == 0)//paran
			suma -= 1 / (double)(n + i*m);
		else
			suma += 1 / (double)(n + i*m);
	}

	cout << "suma je: " << suma << endl;

	system("PAUSE");
	return 0;



}