Rating Scale Calculation excluding the N/A Answer – Cognito Forms

I have created a feedback form in Cognito forms to collect feedback for suppliers. I have a 1-5 rating scale with 14 Questions and a calculation field to calculate the percentage.

I have done the formula and managed to calculate all ratings. I have added the option to N/A to the rating. So I would like to exclude the question answered by N/A from the total number of questions. so the Formula should be if one of the questions is answered by N/A then it should be divided by 13 Questions and not 14.

Current Formula: Total Score / 14 / 5 ( Highest Rating )

Please advise