The error message you're getting is just a warning

I can't tell if your code is complete, or if you're just posting the beginning of it. But the warning is simply saying you're only using 'INPUT' once, meaning you've created it, but are not accessing it.

If you are trying to access INPUT later on in the code, then there must be a typo, just as the warning states, because it's not being accessed after all

Cheers
Sam