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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.
4 isn't the input, it's your returned value, and 3 is the expected value. You can find which input caused it by logging the argument to console.
How? This kata has 111,406 completions.