#include <bits/stdc++.h>
using namespace std;
const int maxn = 1000000 + 10;
char b[maxn];
int a[maxn];
int ccc[20];
int main() {
  long long n;
  long long sum = 0;
  cin >> n;
  if (n % 2 == 0)
    sum = n / 2;
  else
    sum = (-n - 1) / 2;
  cout << sum << endl;
  return 0;
}
