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