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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.
in some test with 123456789 also strange problem:
when i do 123456789 it returns 1234567898 but expected -1
but when i try to return -1 for case 123456789; it's also wrong ))