## Roman Numerals

### March 6, 2009

Roman numerals are a number-notation system developed in classical Rome, chiefly used today to indicate the year in which a motion picture was made, or the sequence number of a Super Bowl.

Roman numerals use letters of the alphabet to indicate numerical value, according to the following code:

I 1    V 5    X 10    L 50    C 100    D 500    M 1000

For example, the number 1732 is represented by Roman numerals as MDCCXXXII, and the number 1956 is represented by Roman numerals as MDCCCCLVI. Letter symbols are normally written from the largest symbol to the smallest, left to right, so the numeric values are additive. However, in order to conserve space, it is permissible to replace four of the same symbol written all in a row in a subtractive manner to the left of a higher-value symbol, so that 1956 may also be represented as MCMLVI, where the CM symbol, with C before M, indicates that C is subtracted from M, and thus indicates the numeric value 900. Wikipedia and MathWorld explain the common usage of Roman numerals.

Your task is to write a function that takes two roman numerals (character strings) as input and returns their sum as a roman numeral as output. Be sure that input can be given in either the additive or subtractive forms of Roman numerals; give output using the subtractive form. What is `add-roman("CCCLXIX", "CDXLVIII")`?

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