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