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);
foreach(var id in callerIds)
Console.WriteLine(id);
}