For a positive integer n, we define a function f:

f (n) = - 1 + 2 - 3 + .. + (- 1) nn

Your task is to calculate f (n) for a given integer n.

Input data
The only line contains a positive integer n (1 ≤ n ≤ 1015).

Output
Output f (n) in a single line.
with c++

#include <iostream>using namespace std;int main() {int n = 0, f = 0, t = 0;cin >> n;if (n <= 1015 && n >= 1) {for (int i = 1; i <= n; ++i) {    t = -i;if (i % 2 == 0) {t = abs(t);}cout << t << " ";f += t;}} else {cout << "Error" << endl;}cout << endl << "Res: " << f;return 0;}