class Queue[+T] (private val l1:List[T] = Nil, private val l2:List[T] = Nil)
{
  class EmptyException(mess:String) extends Exception(mess)

  def enqueue[S>:T](a:S):Queue[S] =
    (this.l1, this.l2) match
    {
     case (Nil, Nil) => new Queue[S](List(a), Nil)
     case (xl,yl) => new Queue[S](xl, a::yl)
    }

  def dequeue():Queue[T] =
    (this.l1, this.l2) match
    {
    case (Nil, Nil) => this
    case (List(sth), yl) => new Queue[T](yl.reverse, Nil)
    case (h::t, yl) => new Queue[T](t, yl)
    case (Nil, h::t) => throw new Exception("To nie jest postać normalna")
    }

  def first():T =
    this.l1 match
    {
    case h::_ => h
    case Nil => throw new EmptyException("Kolejka pusta")
    }

  def isEmpty():Boolean =
    (l1, l2) == (Nil, Nil)
}

var stackOfPoints = new Queue()
var stackOfPixels = new Queue()

object Queue
{
  def apply[T](xs: T*) = new Queue[T](xs.toList.reverse)
}