using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var first = new List<int>{ 1, 2, 3 };

        var second = new List<int>{ 4, 5, 6 };

        foreach(var item in first.Concat(second))

        {

            Console.WriteLine(item);

        }

        Console.WriteLine();    

        foreach(var item in first)

        {

            Console.WriteLine(item);

        }

    }

}