class Stack(object):
    def __init__(self, length):
        self.item = []
        self.length = length

    def push(self, value):
        if self.is_full():
            raise Exception('栈已满')
        else:
            self.item.append(value)

    def pop(self):
        if self.is_empty():
            raise Exception('栈为空')
        return self.item.pop()

    def top(self):
        if self.is_empty():
            raise Exception('栈为空')
        return self.item[-1]

    def is_empty(self) -> bool:
        return len(self.item) == 0

    def is_full(self) -> bool:
        return len(self.item) >= self.length

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