题解 | #【模板】栈#

# 读取输入的操作次数
n = int(input().strip())

# 初始化栈
stack = []

# 处理每个操作

for _ in range(n):
    operation = input().strip().split()

    if operation[0] == 'push':
        # push 操作，将元素入栈
        x = int(operation[1])
        stack.append(x)
    elif operation[0] == 'pop':
        # pop操作，将元素出栈
        if stack:
            print(stack.pop())
        else:
            print('error')
    elif operation[0] == 'top':
        # top 操作，输出栈顶，栈顶不出栈
        if stack:
            print(stack[-1])
        else:
            print('error')