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