def end_game(winner):
    print(winner)
    exit()


game_records = input()
a_score = 0
b_score = 0

for i in range(0, len(game_records), 2):
    if game_records[i] == "A":
        a_score += int(game_records[i + 1])
    else:
        b_score += int(game_records[i + 1])

    if a_score >= 11 and (b_score < 10 or a_score - b_score >= 2):
        end_game("A")
    if b_score >= 11 and (a_score < 10 or b_score - a_score >= 2):
        end_game("B")