I've really learned much more about Gauss integers while solving this problem. I didn't even suspect that most of algebraic theorems and definitions  also take place in complex algebra (I mean Gauss integers, of course). Great thanks to authors for creating that.
For anyway, this test helped me to pass WA#21:
3
2 1 3 5 0 0
4 0 5 0 6 0
0 1 -5 -1 8 12
0 9
One of possible answers is -1 -3