-1
The first thing I would do is convert A,B,C, and D to 1,2,3, and 4. Maybe 0-3, not sure yet. yeah 0,1,2,3. 0,1,2,3 just makes so much more sense than A,B,C,D. Very likely down the road it will prove to be a good move.
Do an ASCII to numeric conversion and subtract x41 or 65 if you are a normal ...