#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n;
  long long int i, odd = 0;
  cin >> n;
  if (n % 2 == 0) {
    cout << n / 2;
  } else {
    odd = (n / 2) + 1;
    cout << -1 * odd;
  }
  return 0;
}
