#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long n;
  cin >> n;
  if (n % 2)
    cout << setprecision(0) << fixed << "-" << ceil((1.0 * n) / 2) << '\n';
  else
    cout << fixed << n / 2 << '\n';
}
int main() { solve(); }
