#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int a, b, c;
  cin >> a;
  b = a % 10;
  c = a / 10;
  if (b == 9)
    cout << -(c * 5 + 5);
  else if (b == 8)
    cout << c * 5 + 4;
  else if (b == 7)
    cout << -(c * 5 + 4);
  else if (b == 6)
    cout << c * 5 + 3;
  else if (b == 5)
    cout << -(c * 5 + 3);
  else if (b == 4)
    cout << c * 5 + 2;
  else if (b == 3)
    cout << -(c * 5 + 2);
  else if (b == 2)
    cout << c * 5 + 1;
  else if (b == 1)
    cout << -(c * 5 + 1);
  else
    cout << c * 5;
  return 0;
}
