题解 | #【模板】栈#

list=[]
y=int(input())
for i in range(y):
    x=input().split()
    if x[0]=='push':
        x[1]=int(x[1])
        list.append(x[1])
    elif x[0]=='pop':
        try:
            print(list.pop(-1))
        except IndexError:
            print('error')
    elif x[0]=='top':
        try:
            print(list[-1])
        except IndexError:
            print('error')