def main():
    S = input()

    actual_idx_sum = 0
    A_apperance = 0
    for idx, letter in enumerate(S):
        if letter == "A":
            actual_idx_sum += idx
            A_apperance += 1

    if A_apperance == 0:
        print(0)
        return

    ideal_idx_sum = A_apperance * (A_apperance - 1) // 2
    print(actual_idx_sum - ideal_idx_sum)


if __name__ == "__main__":
    main()