H
g/[^MDCLXVI]/s///g
# simplify the quirky parts
g/CM/s//CCCCCCCCC/
g/D/s//CCCCC/
g/CD/s//CCCC/
g/XC/s//XXXXXXXXX/
g/L/s//XXXXX/
g/XL/s//XXXX/
g/IX/s//IIIIIIIII/
g/V/s//IIIII/
g/IV/s//IIII/
# convert simplified numerals to integers
g/MMMMMMMMM/s//9/
g/MMMMMMMM/s//8/
g/MMMMMMM/s//7/
g/MMMMMM/s//6/
g/MMMMM/s//5/
g/MMMM/s//4/
g/MMM/s//3/
g/MM/s//2/
g/M/s//1/
v/^[0-9].*$/s/.*/0&/
g/CCCCCCCCC/s//9/
g/CCCCCCCC/s//8/
g/CCCCCCC/s//7/
g/CCCCCC/s//6/
g/CCCCC/s//5/
g/CCCC/s//4/
g/CCC/s//3/
g/CC/s//2/
g/C/s//1/
v/^[0-9]{2}.*$/s/^([0-9])(.*)$/\10\2/
g/XXXXXXXXX/s//9/
g/XXXXXXXX/s//8/
g/XXXXXXX/s//7/
g/XXXXXX/s//6/
g/XXXXX/s//5/
g/XXXX/s//4/
g/XXX/s//3/
g/XX/s//2/
g/X/s//1/
v/^[0-9]{3}.*$/s/^([0-9]{2})(.*)$/\10\2/
g/IIIIIIIII/s//9/
g/IIIIIIII/s//8/
g/IIIIIII/s//7/
g/IIIIII/s//6/
g/IIIII/s//5/
g/IIII/s//4/
g/III/s//3/
g/II/s//2/
g/I/s//1/
v/^[0-9]{4}.*$/s/^([0-9]{3})(.*)$/\10\2/
g/^0+([0-9])/s//\1/
,p
Q