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