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