#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const long long INF = 998244353;
const int N = 100000 + 7;
bool dam[N];
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n;
  cin >> n;
  long long ans = n / 2;
  if (n % 2 == 1) ans = (ans + 1) * -1;
  cout << ans << endl;
  return 0;
}
