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1.) The input parameter num is a number so you can't use split on it. You need to cast it to a string first.

2.) You must return the final answer, not print (puts) it to the console. You need to return the answer as an integer. Input of 3212 must get an output of 9414 only by returning it.

3.) You must return your answer as a number, not a string.

Which programming language?