# No.559 swapAB列
s = input()
#s_after = 'A' * s.count('A') + 'B' * s.count('B')
#print(s_after)
indices = []
hands = 0

for i in range(len(s)):
    if s[i] == 'B':
        indices.append(i + 1)

for j in range(len(indices)):
    hands += len(s) - j - indices[j]

print(hands)