ABOUT RANDOM TEST FAILED!!!!

Finally got it. You should remember, that random test can give you such sequences as:

1. From - to +, e.g. -1, 1, 3, 7 (5 miss)
2. From + to -, e.g. 1, -1, -3, -7 (-5 miss)
3. From zero to smth, e.g. 0, 3, 6, 12 (9 miss)
4. UNCHANGING SEQUENCE, e.g. 2, 2, 2, 2 (2 miss)

I think, most of us got stuck at p.4