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