import re


def crop_title(source: str) -> str:
    """
    Crop out the first title from the source if it starts with it.

    :param source: source string to be processed.

    :returns: source string with the first title removed
    """
    result = source.lstrip()
    if re.match('^#{1,6} .+', result):  # starts with a title
        if '\n' in result:
            return result[result.index('\n') + 1:]
        else:
            return ''
    else:
        return source