helmax - What I'm trying to say is this...try to use the feedback you get when attempting the challenge to help pinpoint where your solution is failing. It can be frustrating, I know, but if you can get creative with your solution (for example, using console.log to see solution output) you can better understand what is and is not working. Hope that helps.

RandyCommas - I ran into the exact same issue. The manner in which I solved it was by altering my function to provide more insight into the test cases. The automated output intentionally leaves out details, but by working with your function, you can use the failed tests to provide debugging feedback.

Hope that is helpful. Good luck.

Gotcha. Thanks.

But if letters is empty, then it won't have a [0], meaning it wil be undefined.

Sorry, Javascript.

what language are you coding in?

This tripped me up too. While it's true the initial number was considered in the description, I also didn't interpret it that way. No worries.