题解 | 【模板】栈的操作

stack = []

q = int(input())

for _ in range(q):
    operate = input().split()

    if operate[0] == 'push':
        x = int(operate[1])
        stack.append(x)

    if operate[0] == 'pop':
        if stack:
            stack.pop()
        else:
            print('Empty')

    if operate[0] == 'query':
        if stack:
            print(stack[-1])
        else:
            print('Empty')
    
    if operate[0] == 'size':
        print(len(stack))