ROMAN_MAP = {
    1000 => "M",
    900 => "CM",
    500 => "D",
    400 => "CD",
    100 => "C",
    90 => "XC",
    50 => "L",
    40 => "XL",
    10 => "X",
    9 => "IX",
    5 => "V",
    4 => "IV",
    1 => "I"
}

def to_arabic(romanian_number)
  result = 0
  str = romanian_number
  ROMAN_MAP.values.each do |roman|
    while str.start_with?(roman)
      result += ROMAN_MAP.invert[roman]
      str = str.slice(roman.length, str.length)
    end
  end
  result
end

puts to_arabic("XX")