题解 | #【模板】栈#

class Stack:
    def __init__(self):
        self.stack=[]
    def push(self,element):
        self.stack.append(element)
    def pop(self):
        if len(self.stack)==0:
            return "error"
        else:
            return self.stack.pop(-1)
    def top(self):
        if len(self.stack)==0:
            return "error"
        else:
            return self.stack[-1]
num = int(input())
st =Stack()
for i in range(num):
    str_num = input()
    str_list = str_num.split(" ")
    if str_list[0]=="push":
        st.push(int(str_list[1]))
    elif str_list[0]=="pop":
        print(st.pop())
    else:
        print(st.top())