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