#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n;
  cin >> n;
  long long int oddsum = 0, evensum = 0, ans = 0;
  long long int p1, p2;
  if (n % 2 != 0) {
    p1 = n / 2 + 1;
    p2 = n / 2;
    oddsum = -(p1 * p1);
    evensum = p2 * (p2 + 1);
  } else {
    p1 = n / 2;
    oddsum = -(p1 * p1);
    evensum = p1 * (p1 + 1);
  }
  ans = oddsum + evensum;
  cout << ans << endl;
  return 0;
}
