题解 | #【模板】栈#

from re import X
n=int(input())
z=[]
for i in range(n):
    do=input()
    if do.startswith("push"):
        x=do.split()
        z.append(int(x[1]))
    elif do=="pop":
        if z==[]:
            print("error")
        else:
            zp=z.pop()
            print(zp)
    elif do=="top":
        if z==[]:
            print("error")
        else:
            print(z[-1])