题解 | #【模板】栈#

import sys
n = int(input())
acts = []
stack = []
for i in range(n):
    acts.append(input().split())
for act in acts:
    if act[0]=='push':
        stack.append(int(act[1]))
    elif act[0]=='pop':
        if len(stack)!=0:
            print(stack.pop())
        else:
            print('error')
    elif act[0]=='top':
        if len(stack)!=0:
            print(stack[-1])
        else:
            print('error')