class StackUnderflowError < RuntimeError
end

class StackOverflowError < RuntimeError
end

class Stack

  def initialize
    @items = []
  end

  def push object
    raise StackOverflowError if @items.length == 10
    @items.push object
  end

  def pop
    raise StackUnderflowError if @items.empty?
    @items.delete @items.last
  end

  def peek
    raise StackUnderflowError if @items.empty?
    @items.last
  end

  def empty?
    @items.empty?
  end

  def full?
    @items.length == 10
  end

end