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

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

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

    private int N;
    private Node first;

    private class Node {
        private Item item;
        private Node next;
    }

    public LinkedStack() {
        first = null;
        N = 0;
        assert check();
    }

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

    public int size() {
        return N;
    }

    public void push(Item item) {
        Node oldfirst = first;
        first = new Node();
        first.item = item;
        first.next = oldfirst;
        N++;
        assert check();
    }

    public Item pop() {
        if (isEmpty()) throw new NoSuchElementException("Stack underflow");
        Item item = first.item;
        first = first.next;
        N--;
        assert check();
        return item;
    }


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

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

    private boolean check() {
        if (N == 0) {
            if (first != null) return false;
        }
        else if (N == 1) {
            if (first == null)      return false;
            if (first.next != null) return false;
        }
        else {
            if (first.next == null) return false;
        }
        int numberOfNodes = 0;
        for (Node x = first; x != null; x = x.next) {
            numberOfNodes++;
        }
        if (numberOfNodes != N) return false;
        return true;
    }

    public static void main(String[] args) {
        LinkedStack<String> s = new LinkedStack<String>();
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            if (!item.equals("-")) s.push(item);
            else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
        }
        StdOut.println("(" + s.size() + " left on stack)");
    }
}