def most_minutes_asleep(naps):
    """ Return the ID of the guard who naps the most. """
    most_minutes = 0
    sleepiest = None
    for guard, recorded_naps in naps.items():
        total = 0
        for nap in recorded_naps:
            total += nap[1] - nap[0]
        if total > most_minutes:
            most_minutes = total
            sleepiest = guard

    return sleepiest