def parse_input(input_file):
    """
    Processes the input with song titles.
    See above format.

    Returns a dict of mapping number -> [title1, title2, ...]
    """
    tdb = {}
    disc_no = -1
    with open(input_file) as fin:
        for line in fin:
            line = line.strip()
            if 'disc ' in line.lower() or 'disk ' in line.lower():
                disc_no += 1
                tdb[disc_no] = []
            elif line != '':
                tdb[disc_no].append(line)

    return tdb