#include <bits/stdc++.h>
using namespace std;
const int INF = 1000000000;
const int MOD = 1000000000;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  long long N;
  cin >> N;
  if (N % 2 == 0)
    cout << (N / 2);
  else
    cout << ((-1 * (N / 2)) - 1);
}
