using System;

using System.Collections.Generic;

public class Program

{

    public class TreeNode 

    {

        public int val;

        public TreeNode left;

        public TreeNode right;

        public TreeNode(int val, TreeNode left = null, TreeNode right = null) 

        {

            this.val = val;

            this.left = left;

            this.right = right;

        }

    }

    public static List<int> LonelyNodes;

    public static IList<int> GetLonelyNodes(TreeNode root) {

        LonelyNodes = new List<int>();

        if (root == null)

            return LonelyNodes;

        Helper(root);

        return LonelyNodes;

    }

    public static void Helper(TreeNode node)

    {

        if (node == null)

            return;

        if (node.left == null && node.right != null)

            LonelyNodes.Add(node.right.val);

        if (node.left != null && node.right == null)

            LonelyNodes.Add(node.left.val);

        Helper(node.left);

        Helper(node.right);

    }

    public static void Main()

    {

        Console.WriteLine("UniLecs");

        // test

        var root = new TreeNode(2);

        root.left = new TreeNode(7);

        root.right = new TreeNode(5);

        root.left.left = new TreeNode(2);

        root.left.right = new TreeNode(6);

        root.left.right.left = new TreeNode(5);

        root.left.right.right = new TreeNode(11);

        root.right.right = new TreeNode(9);

        root.right.right.left = new TreeNode(4);

        Console.WriteLine(string.Join(", ", GetLonelyNodes(root))); // [9, 4]

    }

}