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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.
That depends on how the tests, and in particular, the error messages are written.
Print the input and fix your code. It fails with inputs like
"2". Not a kata issue.