#include <bits/stdc++.h>
int main(void) {
  unsigned long long int n;
  scanf("%llu", &n);
  if (n == 1)
    printf("%d", -1);
  else if (n % 2 == 0)
    printf("%llu", n / 2);
  else
    printf("%lli", (n - 1) / 2 - n);
  return 0;
}
