def correct_invalid_start(self, scansion: str) -> str:
        """
        The third syllable of a hendecasyllabic line is long, so we will convert it.

        :param scansion: scansion string
        :return: scansion string with corrected start

        >>> print(HendecasyllableScanner().correct_invalid_start(
        ... "- U U  U U  - U   -  U - U").strip())
        - U -  U U  - U   -  U - U
        """
        mark_list = string_utils.mark_list(scansion)
        vals = list(scansion.replace(" ", ""))
        corrected = vals[:2] + [self.constants.STRESSED] + vals[3:]
        new_line = list(" " * len(scansion))
        for idx, car in enumerate(corrected):
            new_line[mark_list[idx]] = car
        return "".join(new_line)