Put a "- 8" object after the first outlet, and don’t after the second. Connect both outlets to the same place afterwards.
However, I doubt this will work recursively, if that’s what you want (for instance, 35 would only become 27, and it would probably stack overflow.) the Modulo operator might be more what you’re looking for?
Type "% 9" into an object box (no quotes, of course), and anything you pass through it will be remaindered to be between 0 and 8. In our previous example, 35 would become the number 8. "% 10" will go between 0 and 9.
Here’s a quick patch to illustrate that:
— Pasted Max Patch, click to expand. —
Copy all of the following text. Then, in Max, select New From Clipboard.