File name usage

Does anyone know of a VBA routine that will read the last character of a SolidWorks drawing file name? We use that last character before the ".slddrw" as our revision letter/number. I want to force two custom property fields to read and display this value to automatically update those fields in the title block. Here is the example:

####-XX-XX-###-rA.slddrw

I want the custom property fields to read the character in the "A" position.

SolidworksDrawings And Detailing