def vnu(cards):
    """Value and whether or not there is a usable ace."""
    s = 0
    aces = 0
    for card in cards:
        if card[0] == 'A':
            aces += 1
        else:
            s += int(card)
    acevals = [11 for ace in range(aces)]
    while (s + sum(acevals) > 21) and (11 in acevals):
        i = acevals.index(11)
        acevals[i] = 1
    s = s + sum(acevals)
    if s <= 21:
        return s, (11 in acevals)
    else:
        return -1, False