Hi this is one of the first problems I've done and for some reason, I got the error NZEC. Could someone explain what it means and why I got it. Here is my code, it is submission number 728302.

num=input()
for z in range():
    a=raw_input()
    x=int(a)+1
    while a:
        a=str(x)
        if a==a[::-1]:
            print a
            break
        else:
            x=x+1

Please help I've tried everything but it won't go through.