def __eq__(self, other):
        return (isinstance(other, self.__class__) and
                other.package == self.package)
def kth(root, k):
    if k < size(root.left):
        return kth(root.left, k)
    elif k > size(root.left):
        return kth(root.right, k - size(root.left) - 1)
    return root.key