Tests aren't really strong in my opinion. I coded a correct (but a little too slow) solution, which gave time limit on test 10. Then I just ignored the cases, where the first object's number is divisible by 7 and it ran in time (1/7 time optimization), and got accepted. But if we have tests, whose answers are 1 x, 2 x, 3 x, ... , 10 x (for example) this solution will fail.