def main():
    values = list(input())
    #print(values)
    count = 0

    while not check(values):
        sorted_values = sort_values(values)
        count += 1

    print(count)

def check(values):
    if sorted(values) == values:
        return True
    else:
        return False

def sort_values(values):
    last_B_pos = -1
    for i, v in enumerate(values):
        if v == 'A':
            if last_B_pos >= 0:
                if last_B_pos + 1 == i:
                    values[last_B_pos] = 'A'
                    values[i] = 'B'
                    return values
        else:
            last_B_pos = i

if __name__ == '__main__':
    main()