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