code: def correct_invalid_start(self, scansion: str) -> str:
          
          mark_list = string_utils.mark_list(scansion)
          raw_scansion = scansion.replace(" ", "")
          if raw_scansion.startswith(self.constants.SPONDEE + self.constants.UNSTRESSED):
              new_scansion = list(self.constants.SPONDEE + self.constants.SPONDEE + raw_scansion[4:])
              corrected = "".join(new_scansion)
              new_sequence = list(" " * len(scansion))
              for idx, car in enumerate(corrected):
                  new_sequence[mark_list[idx]] = car
              return "".join(new_sequence)
          return scansion
docs: If a hexameter, hendecasyllables, or pentameter scansion starts with spondee,
          an unstressed syllable in the third position must actually be stressed,
          so we will convert it: - - | U    ->  - - | -
  
          :param scansion:
          :return:
  
          >>> print(VerseScanner().correct_invalid_start(
          ... " -   - U   U -  -  U U U U  U U  - -").strip())
          -   - -   - -  -  U U U U  U U  - -