题解 | 【模板】栈的操作

seq=[]
num=int(input())
for _ in range(num):
    parts=input().split()
    op=parts[0]
    if op=="push":
        seq.append(parts[1])
    elif op=="pop":
        if seq != []:
            seq.pop()
        else:
            print("Empty")
    elif op=="query":
        if seq != []:
            print(seq[-1])
        else:
            print("Empty")
    elif op=="size":
        print(len(seq))