sed '1d
:
s/CM/CCCCCCD/
s/CD/CCCC/
s/XC/XXXXXXL/
s/XL/XXXX/
s/IX/IIIIIIV/
s/IV/IIII/
t
:0
s/\([^M]\)\([MD]\)/\2\1/
s/\([LXVI]\)\([CL]\)/\2\1/
s/\([VI]\)\([XV]\)/\2\1/
s/ //
s/IIIII/V/
s/VV/X/
s/XXXXX/L/
s/LL/C/
s/CCCCC/D/
s/DD/M/
t0
s/CCCC/CD/
s/DCD/CM/
s/XXXX/XL/
s/LXL/XC/
s/IIII/IV/
s/VIV/IX/
/MMMM/cERROR'