Sum of numbers of same cell and the result will be 0 to 9 or 11, 22, 33 or 44

Hi,
I would like to know if you could help me create one formula to excel.
I would like to make a sum of each number of same cell.
The sum has to have the result of 0 to 9 or 11 or 22 or 33 or 44.
For example: If the cell has the number 911. The sum will be 9+1+1=11
For example if the number is 9996=9+9+9+6=33
For example if the number is 23564=2+3+5+6+4=20=2+0=2
For example if number is 466692=4+6+6+6+9+2=33
In this moment I use this formula:
=If(REST(A1;9)=0;“9”;REST(A1;9)) (but the result will be from 0 to 9)
I need to add the exception if the result is 11 or 22 or 33 or 44
Can anyone help me?
I have the formula I can cover also the result of 11 but I need also to 22 or 33 or 44
=IF(A1=11;11;IF(REST(A1;9)=0;“9”;REST(A1;9)))
Thanks.
Best regards

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I have the same question in https://www.excelforum.com/excel-fo...esult-will-be-0-to-9-or-11-22-33-or-44-a.html
Can anyone help me? Thanks.

I have this question also in
https://www.mrexcel.com/forum/excel...-same-cell-result-will-0-9-11-22-33-44-a.html

Thank you.