题解 | #【模板】栈#

a = int(input())
b = []
for j in range(a):
    i = input().split()

    if str(i[0]) == "push":
        b.append(i[1])
    if str(i[0]) == "pop":
        if b:
            print(b.pop())
        else:
            print("error") 
    if str(i[0]) == "top":
        if b:
            print(b[-1])
        else:
            print("error")