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