Sequential ID numbers generated for non-blank fields

[exceler_52]

I've done a lot of looking around and found some formulas and scripts that are close to what I need, but nothing close enough that I can mold it to my needs. I have a list of points (column C) with a column on each side indicating whether the point is an input (column B) and/or an output (column D). I need something that will generate strings in columns A & E that begin with a text prefix followed by an incremented four digit sequential ID and skips blanks like the below example. Any suggestions?

example.jpg