I had the same problem. I was getting NumberFormatExceptions because I was trying to parse an integer that was greater than the integer max value. My advice to anyone with this issue: Try refactoring your code to use strings instead of integers where possible (any more of a hint would spoil the answer.)

Don't include main function in your code. The tests call your function is_valid_ip and check the value it returns.

Please say which language you're using and give more concrete elements, it's hard to help otherwise. You should read this: https://docs.codewars.com/training/troubleshooting/

And they are right.

I am getting the same error they are saying -5 is not a prime .

a prime number (or a prime) is a natural number greater than 1...

No, it isn't.