#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int i, j, k, n, m, r, s;
  cin >> n;
  if (n % 2 == 0) {
    m = n / 2;
  } else {
    m = n - 1;
    m = m / 2 - n;
  }
  cout << m << endl;
}
