sum up to maximum value

Good evening. I am relatively new to excel formulas and looking to understand how to get what is in my head into a workable formula.

1. THE ISSUE
The values in the "N" column represent the actual value that was entered.
The values in the "O" column represent how much those values are increasing.

The value in "P" is obviously the SUM of "N" and "O", which is fine, until it goes over the number "10" which I would like to set as a metaphorical "threshold".

2. WHAT I WANT THE FORMULA TO SAY (I think)

IF "P" exceeds "10.00," then round down to "10.00"

OR

IF "P" exceeds "10.00," then display "10.00"

I DO NOT want it to affect any other values, only the "P" column

How would I write this?
Thanks!

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