class tree:
  def __init__(self):
    self.empty = True

  def show(self):
    if self.empty:
      return
    self.left.show()
    print(self.data)
    self.right.show()

  def add(self, v):
    if self.empty:
      self.empty = False
      self.data = v
      self.left = tree()
      self.right = tree()
    elif v < self.data:
      self.left.add(v)
    else:
      self.right.add(v)