In wikipedia Roman numerals, it is clearly stated that
- I placed before V or X indicates one less, so four is IV (one less than five) and nine is IX (one less than ten)
- X placed before L or C indicates ten less, so forty is XL (ten less than fifty) and ninety is XC (ten less than a hundred)
- C placed before D or M indicates a hundred less, so four hundred is CD (a hundred less than five hundred) and nine hundred is CM (a hundred less than a thousand)
Therefore, test cases like "IL", "IM" should be the same as "LI", "MI", which are 51 and 1001, respectively.