# iterarive version

class ListNode:

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

class Stack:

    def __init__(self):
        self.top = None
        self.count = 0

    def push(self, value):
        node = ListNode(value, self.top)
        self.top = node
        self.count += 1

    def is_empty(self):
        return self.top is None

    def pop(self):
        if not self.is_empty():
            current_top = self.top
            self.top = self.top.next
            return current_top.value

    def depth(self):
        if self.is_empty():
            return 0
        else:
            return print(self.count)

c = Stack()
c.push(12)
c.push("Hello")
c.push(34)
c.depth()