import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        for (int i = 1; i <= n*2; i++) {
            if (i % 2 == 0 && i % n == 0) {
                System.out.println(i);
                break;
            }
        }
    }
}
