input: Write a python function to convert a roman numeral string to an integer.
  assert romanToInt('III') == 3
  assert romanToInt('IV') == 4
  assert romanToInt('IX') == 9
  assert romanToInt('LVIII') == 58
  assert romanToInt('MCMXCIV') == 1994
output: def romanToInt(s: str) -> int:
      roman_values = {
          'I': 1, 'V': 5, 'X': 10, 'L': 50,
          'C': 100, 'D': 500, 'M': 1000
      }
      
      total = 0
      prev_value = 0
      
      for char in reversed(s):
          value = roman_values[char]
          if value < prev_value:
              total -= value
          else:
              total += value
          prev_value = value
      
      return total