Reverse Roman Numerals Reverse Roman Numerals

In the CheckiO mission Roman Numerals you have to convert a decimal number into its representation as a roman number.
Here you have to do the same but the other way around.

You are given a roman number as a string and your job is to convert this number into its decimal representation.

A valid roman number, in the context of this mission, will only contain roman numerals as per the below table and follows the rules of the substractive notation.
Check this Wikipedia article for more details about how to form roman numerals.

I1 (unus)
V5 (quinque)
X10 (decem)
L50 (quinquaginta)
C100 (centum)
D500 (quingenti)
M1,000 (mille)

Input: A roman number as a string.

Output: The decimal representation of the roman number as an int.


reverse_roman('VI') == 6
reverse_roman('LXXVI') == 76
reverse_roman('CDXCIX') == 499
reverse_roman('MMMDCCCLXXXVIII') == 3888

len(roman_string) > 0
all(char in "MDCLXVI" for char in roman_string) == True
0 < reverse_roman(roman_string) < 4000