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