Roman Numeral Grammar (up to C)

roman-numeral
   one-to-nine
   tens
   tens one-to-nine
   C
   
ones
   I
   II
   III

one-to-four
   ones
   IV
   
one-to-nine
   one-to-four
   V
   V ones
   IX

tens
   X
   XX
   XXX
   XL
   L
   LX
   LXX
   LXXX
   XC