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