#include <bits/stdc++.h>
using namespace std;
long long n;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  if (n == 0)
    cout << 0 << endl;
  else if (n % 2 == 0)
    cout << n + 1 << endl;
  else
    cout << (n + 1) / 2 << endl;
  return 0;
}
