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