class QueueItem {
    int data;
    class QueueItem next;
    class QueueItem prev;
  
    void Init(int data, class QueueItem next, class QueueItem prev) {
        this.data = data;
        this.next = next;
        next.prev = this;
        this.prev = prev;
        prev.next = this;
    }
    int GetData() {
        return this.data;
    }
    class QueueItem GetNext() {
        return next;
    }
    class QueueItem GetPrev() {
        return prev;
    }
    void SetNext(class QueueItem n) {
        next = n;
    }
    void SetPrev(class QueueItem p) {
        prev = p;
    }
}

class Queue {
    int sp;
    class QueueItem head;
  
    void Init() {
        this.head = new QueueItem();
        this.head.Init(0, this.head, this.head);
    }
    void EnQueue(int i) {
        class QueueItem temp;
        temp = new QueueItem();
        temp.Init(i, this.head.GetNext(), this.head);
    }
    int DeQueue() {
        int val;
        if (this.head.GetPrev() == this.head) {
            Print("Queue Is Empty");
            return 0;
        } else {
            class QueueItem temp;
            temp = this.head.GetPrev();
            val = temp.GetData();
            temp.GetPrev().SetNext(temp.GetNext());
            temp.GetNext().SetPrev(temp.GetPrev());
        }
        return val;
    }
}

class Main {
    static void main() {
        class Queue q;
        int i;
        q = new Queue();
        q.Init();
        for (i = 0; i < 10; i = i + 1)
            q.EnQueue(i);

        for (i = 0; i < 4; i = i + 1)
            Print(q.DeQueue(), " ");
        Print("\n");

        for (i = 0; i < 10; i = i + 1)
            q.EnQueue(i);
        for (i = 0; i < 17; i = i + 1)
            Print(q.DeQueue(), " ");
        Print("\n");
    }
}