I like the method you wrote and it’s helpful for understanding how not to write clunky 109 line programs like I did for this one, but arriving at MIM for 1999 is not correct for the way Roman numerals work, as ones, tens, etc. are treated as separate units.
http://www.web40571.clarahost.co.uk/roman/1999.htm
I was a little confused and maybe some brief explanation of this could be helpful. The previous method does return the result I bumbled my way into.
Thanks for the great book!