#include <bits/stdc++.h>
using namespace std;
void fscan(long long int &number) {
  bool negative = false;
  register int c;
  number = 0;
  c = getchar();
  if (c == '-') {
    negative = true;
    c = getchar();
  }
  for (; (c > 47 && c < 58); c = getchar()) number = number * 10 + c - 48;
  if (negative) number *= -1;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n, sum = 0;
  fscan(n);
  if (n % 2 == 1)
    sum = (-n - 1) / 2;
  else
    sum = n / 2;
  cout << sum;
  return (0);
}
