using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Queue<int> callerIds = new Queue<int>();

        callerIds.Enqueue(1);

        callerIds.Enqueue(2);

        callerIds.Enqueue(3);

        callerIds.Enqueue(4);

​

        Console.WriteLine(callerIds.Contains(2)); //true

        Console.WriteLine(callerIds.Contains(10)); //false

​

    }

}