The largest valid response in this thread, +1.
That's a paradox.
Unless you're acknowledging that your response will not be valid. Because if yours is valid, then you will have to add 1 ad infinitum.
Only if you insist on looping over this for no reason.
Run through the thread and find the largest valid response. (It isn't mine to start with, because "The largest Valid Response in this Thread" is not, by itself, a number.) Take that value, add 1.
Operation complete, there is no reason to repeat the procedure.