# Homework 26, challenge -- solution.

class Stack:
    def __init__(self):
        self.items = []

    def push(self, v):
        self.items.append(v)

    def pop(self):
        return self.items.pop()

    def peek(self):
        if self.items:
            return self.items[-1]
        return None

    def size(self):
        return len(self.items)

stack = Stack()
stack.push("a")
stack.push("b")
stack.push("c")
print(stack.size())    # 3
print(stack.peek())    # c
print(stack.pop())     # c
print(stack.pop())     # b
print(stack.size())    # 1