Implement a function that takes a Roman numeral as its argument and returns its value as an integer. You don't need to validate the form of the Roman numeral.

Modern Roman numerals are written by expressing each digit of the number to be encoded separately, starting with the leftmost digit and skipping any 0s. So 1990 is rendered "MCMXC" (1000 = M, 900 = CM, 90 = XC) and 2008 is rendered "MMVIII" (2000 = MM, 8 = VIII). The Roman numeral for 1666, "MDCLXVI", uses each letter in descending order.

Here's a chart to help out:

Symbol    Value
I          1
V          5
X          10
L          50
C          100
D          500
M          1,000

Example

solution('XXI'); // should return 21

Tests

solution('I')
solution('IV')
solution('MMVIII')
solution('MDCLXVI')

Good luck!

This challenge comes from jhoffner on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

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