Check folder for #of files in series

[Ed]

I parse a .txt database output into about 8,000 Word documents. Each doc is
named by its report number, which always begins with "L5-*" - "*" being a
different letter. Can a macro be created that will look into the folder
containing these reports and counthow many are in each series (how many
L5-A, L5-B, etc.)? What functions would I look at? And how do you
increment a letter for a loop? Can you say "A+1"?

Thanks for helping.
Ed