#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n;
  cin >> n;
  if (n % 2 == 0)
    cout << n * (n + 2) / 4 - n * n / 4;
  else
    cout << (((n - 1) / 2) * ((n + 1) / 2)) - (((n + 1) / 2) * ((n + 1) / 2));
}
