// Project Recursive
// Class Main

// Practice problem: predict the output by first
// drawing the recursion tree.

public class RecursiveTrace
{
    public static void main(String[] args)
    {
        f(3);
    }

    public static void f(int n)
    {
        if (n > 0)
        {
            System.out.print(n + " ");
            f(n - 1);
            System.out.print(n + " ");
            f(n - 2);
            System.out.print((n + 1) + " ");
        }
    }
}