Hi Aziz,
The error is because you are giving input string/char to airthmetic function.
Please try to perform below check before input to airthmatic function.
Input --> mapWithDefault (blank) --> equal --> Blank (constant) --> Not (Boolean function)
then perforn the airthmatic operation.
If you do not want to perform this many validation in graphical mapping the use the UDF.
Regards,
Harish