// Esta é uma cópia de algs4/Queue.java
// de Sedgewick e Wayne
// sem os comentários

import java.util.Iterator;
import java.util.NoSuchElementException;

public class Queue<Item> implements Iterable<Item> {

    private int N;
    private Node<Item> first;
    private Node<Item> last;

    private static class Node<Item> {
        private Item item;
        private Node<Item> next;
    }

    public Queue() {
        first = null;
        last  = null;
        N = 0;
    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return N;     
    }

    public Item peek() {
        if (isEmpty()) 
            throw new NoSuchElementException("Queue underflow");
        return first.item;
    }

    public void enqueue(Item item) {
        Node<Item> oldlast = last;
        last = new Node<Item>();
        last.item = item;
        last.next = null;
        if (isEmpty()) first = last;
        else           oldlast.next = last;
        N++;
    }

    public Item dequeue() {
        if (isEmpty()) 
            throw new NoSuchElementException("Queue underflow");
        Item item = first.item;
        first = first.next;
        N--;
        if (isEmpty()) last = null;
        return item;
    }

    public String toString() {
        StringBuilder s = new StringBuilder();
        for (Item item : this)
            s.append(item + " ");
        return s.toString();
    } 

    public Iterator<Item> iterator()  {
        return new ListIterator<Item>(first);  
    }

    private class ListIterator<Item> implements Iterator<Item> {
        private Node<Item> current;

        public ListIterator(Node<Item> first) {
            current = first;
        }

        public boolean hasNext() { 
            return current != null;                     
        }

        public void remove() { 
            throw new UnsupportedOperationException();  
        }

        public Item next() {
            if (!hasNext()) throw new NoSuchElementException();
            Item item = current.item;
            current = current.next; 
            return item;
        }
    }

    public static void main(String[] args) {
        Queue<String> q = new Queue<String>();
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            if (!item.equals("-")) q.enqueue(item);
            else if (!q.isEmpty()) StdOut.print(q.dequeue() + " ");
        }
        StdOut.println("(" + q.size() + " left on queue)");
    }
}