#include <bits/stdc++.h>
using namespace std;
int main() {
  int sum = 0;
  long long number;
  cin >> number;
  if (number % 2 == 0) {
    number = number / 2;
    cout << number << endl;
  } else {
    number = (number + 1) / 2;
    number = number * -1;
    cout << number << endl;
  }
}
