z-xcorr

Why is my code failing for last test case any help?
http://www.z-trening.com/new/www/html/submit.php?submit=7100053731&subm_code=1

Why 'int smat [ 512 ] [ 512 ];' Try 'int smat [ 1024 ] [ 1024 ];' Initialy increase rez (2000000000).

And include +/- 15 in your solution.

I don't understand, why to add 15 ?

Thanks it passed!