getE2

#include <iostream>
using namespace std;

int getE()
{
    int n, s = 1, e = 0;
    cout << "n="; cin >> n;
    for (int x = 2; x <= n * 2; x += 2, s = -s)
    {
        e += x * s;
    }

   return e;
}

int main()
{
    cout << getE();
    return 0;
}