def METHOD_NAME(dti, start, length):
    """Return start and end dates of a sequence as tuple
    :param <DateTimeIndex> dti: datetime series of working days
    :param <int> start: index of start
    :param <int> length: number of sequential days
    :return <Tuple[pd.Timestamp, pd.Timestamp]>: tuple of start and end date
    """
    tup = (dti[start], dti[start + (length - 1)])
    return tup