using System;

using System.Collections.Generic;   

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        List<int> data1 = new List<int> {1,2};

  List<int> data2 = new List<int>{1,2,3,4};

​

  var result = data2.Except(data1);

        foreach(var i in result){

            Console.WriteLine(i);

        }

    }

}