def scan_frame(reference_start):
    """
    Find the frame of a sequencing using the alignment starting position

    :param int reference_start: Alignment start position
    :return: Number of bases to slice sequence to make it in-frame
    :rtype: int
    """
    in_frame_adjustment = 0
    while (reference_start + in_frame_adjustment) % 3 != 0:
        in_frame_adjustment += 1

        if in_frame_adjustment > 3:
            return

    return in_frame_adjustment