using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List<int> numbers1 = new List<int> { 1, 2, 3 };
        List<int> numbers2 = new List<int> { 4, 5, 6 };

        var combinedNumbers = numbers1.Concat(numbers2);

        foreach (var number in combinedNumbers)
        {
            Console.WriteLine(number);
        }
    }
}

1
2
3
4
5
6