题解 | 【模板】栈的操作

import sys

input = sys.stdin.readline

n = int(input())
output=[]
stack = []

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

    if line.startswith("push"):
        _, x = line.split()
        stack.append(x)

    elif line == "pop":
        if stack:
            stack.pop()
        else:
            output.append("Empty")

    elif line == "query":
        if stack:
            output.append(stack[-1])
        else:
            output.append("Empty")

    elif line == "size":
        output.append(str(len(stack)))
        
print('\n'.join(output))