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