class Node:
    def __init__(self,  data=None, next=None):
        self.data = data
        self.next = next


class OneWayList:
    def __init__(self):
        self.length = 0
        self.top = None

    def push(self, e):
        node = Node(e)
        if self.length == 0:
            self.top = node
        else:
            node.next = self.top
            self.top = node
        self.length += 1
    def pop(self):
        if self.length > 0:
            tmp = self.top.next
            del self.top
            self.top = tmp
            self.length -= 1