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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
See the fork with format checking ;-)
https://www.codewars.com/kumite/58b942c0764c412926000087?sel=5a0aa3d48ba91469a60000a5
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Agree with the other comments, which just leaves me to suggest that it'd also fail with an input of 0 (zero) (or 00) which ought to return None but which would return 0