@atenea_nature, you mean to use Math.toIntExact() instead of Math.round() for calculations ?

Math.round gives a long, you need to use toInt(). At least I solved the problem that way

For Regex learning: https://www.regular-expressions.info/tutorial.html
For Regex testing/debugging: https://regex101.com/
For Streams: https://www.youtube.com/watch?v=f5j1TaJlc0w - there are more similar tutorials on the YT, if you don't know lambas - learn them first.

Issue with your code is not a kata issue! When I ran your code, there's division by zero error, so your logic is wrong! And you don't need to include main in your solution, FYI!

Being frustrated is not a kata issue, sorry.
BTW there is no need to round everywhere... Did you read the details of the example?