using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

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

        var result = new List<int>();

        var temp = source.Where(x => !result.Contains(x));      

        result.AddRange(temp);      

        Console.WriteLine(result.Count());

        var result2 = new List<int>();

        var temp2 = source.Where(x => !result2.Contains(x)).ToList();

        result2.AddRange(temp2);        

        Console.WriteLine(result2.Count());

    }

}