not an issue, use the question tag to ask for help

I mean, it's not a common knowledge if it's limited to English, is it?

I am not arguing with language. I am just pointing out that meaning of the discussed word is totally NOT a common knowledge, and it can be ambiguous for worldwide audience, and only people focused on one of possibilities, a very specific one, somehow miss the ambiguity.

I'm reading the Kata's description in English.

https://www.etymonline.com/word/-teen

There's the origin of the word "teen"

Only in English.

"Ten, Eleven, Twelve" does not end in "teen".

thirTEEN does...

This is common knowledge... correct?

[Citation needed]

https://en.wikipedia.org/wiki/Teenager_(disambiguation)

Where is this definition coming from ?!?

That code will fail in your machine too when calling your function several times, read this

• on your machine, invoke your function twice one time after another in one run. It will also fail on your machine.
• even if you fix this problem, your solution probably will be too slow.

Please read this: https://github.com/codewars/codewars.com/wiki/Markdown-Formatting#block-code-formatting

Until then it's difficult to tell what's wrong with your code, but global variable definitely does not help.

Hey, you should use the question label for help and post all your code inside the three back-ticks.
But anyway, you are going to have to think of an approach without for loops. Have a read below. You need a solution which is just as quick for large numbers as small ones...something more mathsy :)