题解 | 【模板】栈的操作

def main():
    n=int(input())
    stack=[]
    for _ in range(n):
        line=input().split()
        command=line[0]

        if command=="push":
            x=int(line[1])
            stack.append(x)
        elif command=="pop":
            if not stack:#if stack==[]
                print("Empty")
            else:
                stack.pop()
        elif command=="query":
            if not stack:
                print("Empty")
            else:
                print(stack[-1])
        elif command=="size":
            print(len(stack))
    
main()