S = raw_input()
if S.count('A') == 0 or S.count('B') == 0:
    print 0
else:
    tmp = 0
    ans = 0
    for i in xrange(len(S)-1, -1, -1):
        if S[i] == 'A':
            tmp += 1
        else:
            ans += tmp
            tmp = 0
    print ans