using System;

using System.Linq;

using System.Collections.Generic;

​

public class Person

{

    public int ID { get; set; }

}

​

public class Program

{

    public static void Main()

    {

        List<Person> peopleList1 = new List<Person>();

        peopleList1.Add(new Person() { ID = 1 });

        peopleList1.Add(new Person() { ID = 2 });

        peopleList1.Add(new Person() { ID = 3 });

​

        List<Person> peopleList2 = new List<Person>();

        peopleList2.Add(new Person() { ID = 1 });

        peopleList2.Add(new Person() { ID = 2 });

        peopleList2.Add(new Person() { ID = 3 });

        peopleList2.Add(new Person() { ID = 4 });

        peopleList2.Add(new Person() { ID = 5 });

​

        Print(peopleList1);

        Print(peopleList2);

​

        var personList = peopleList2.Where(p => !peopleList1.Any(s => s.ID==p.ID)).ToList();

        Print(personList);

        // Get IDs as list

        var numbers = personList.Select(s=>s.ID).ToList();

        foreach(var num in numbers){

            Console.WriteLine(num);

        }

    }

​

    private static void Print(List<Person> list)

    {

        foreach (var document in list)

        {

            Console.WriteLine(document.ID);

        }

        Console.WriteLine("=====================\n");

    }

}