Counting until a condition and then, again counting from start

Hello All,
This is my first post to any forum. I am seriously got stuck at this problem. Experts! please help me.

Problem: I want to count "P" till "A" comes and then again I want to start counting "P" from beginning.
I have attached the sheet for your working

Please suggest me some way to solve it (would be better if you avoid 'Macros' as I have no knowledge about it)

Amit