KTV

class Node(object):
    __slots__ = ('val', 'next')

    def __init__(self, val):
        self.val = val
        self.next = None

    def set_link(self, node):
        self.next = node


class List(object):
    __slots__ = ('head',)

    def __init__(self):
        self.head = None

    def append(self, val):
        node = Node(val)
        if self.head is None:
            self.head = node
        else:
            node.set_link(self.head)
            self.head = node

    def echo(self):
        el = self.head
        while el is not None:
            print(el.val)
            el = el.next

    def reverse(self):
        pass