Create a function taking a non-negative integer as its parameter and returning a string containing the Roman Numeral representation of that integer.

By convention, "modern" Roman numerals are written by expressing each digit separately starting with the leftmost digit and skipping any digit with a value of zero.

Examples

• If n is 1990 then romStr = 'MCMXC' since 1000=M, 900=CM, 90=XC.
• If n is 2008 then romStr = 'MMVIII' since 2000=MM, 8=VIII.
• If n is 1666 then romStr = 'MDCLXVI'.
• If n is 0 then romStr is empty ([] and '' are both acceptable)

n will always be an integer between 0 and 3999 (inclusive).

This problem is adapted from Rosetta Code.