using System;

using System.Collections.Generic;

 using System.Linq; 

public class Program

{

    public static void Main()

    {

        List<int> oldNumber = new List<int>() 

        {

            1, 2, 3, 4, 5, 6, 7, 8, 9, 10

        };

​

        List<int> newNumber = new List<int>() 

        {

            0, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12

        };

        List<int> addedNumber = oldNumber.Except(newNumber).ToList();

        Console.WriteLine(addedNumber);

    }

}