Frog River One Codility test ,weird error

I try to solve this Codility task (because i have to do a test with a software house company), but i found a weird error:

Analysis summary
The following issues have been detected: wrong answers.

For example, for the input (2, [2, 2, 2, 2, 2]) the solution returned a wrong answer (got 0 expected -1).

I don't understand why he expects -1 instead of 0 and also he says my test is good if i insert (2, [2, 2, 2, 2, 2]) before to check out my solution.

Suggestions?