using System;

​

public class Program

{

    public Node tree;

    public static int Maxlevel = 0;

    public class Node

    {

        public int data;

        public Node leftchild;

        public Node rightchild;

        public Node(int d)

        {

            data = d;

            leftchild = rightchild = null;

        }

    }

​

    public void LeftChild(Node root, int level)

    {

        if (root == null)

        {

            return;

        }

​

        if (Maxlevel < level)

        {

            Console.Write("{0},", root.data);

            Maxlevel = level;

        }

​

        LeftChild(root.leftchild, level + 1);

        LeftChild(root.rightchild, level + 1);

    }

​

    public static void Main()

    {

        Program program = new Program();

        program.tree = new Node(1);

        program.tree.leftchild = new Node(2);

        program.tree.rightchild = new Node(3);

        program.tree.leftchild.rightchild = new Node(4);

        program.tree.leftchild.rightchild.rightchild = new Node(5);

        program.tree.leftchild.rightchild.rightchild.rightchild = new Node(6);

        program.tree.leftchild.rightchild.rightchild.rightchild.rightchild = new Node(7);

        program.LeftChild(program.tree, 1);

    }

}