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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.
Unfortunately, your algorithm is too slow. Try to solve it using number theory! (^^)
By the way, there's no need to use multithreading.
All you need is code formatting and a spoiler flag when posting code :D