S = input()
def solve(S):
    if (len(S) == 1):
        return 0
    ordA = [-1] * len(S)
    ordB = [-1] * len(S)
    oA = 0
    oB = len(S) - 1
    for i in range(0, len(S)):
        if S[i] == 'A':
            ordA[i] = oA
            oA += 1
    for i in range(len(S) - 1, -1, -1):
        if S[i] == 'B':
            ordB[i] = oB
            oB -= 1
    ansA = 0
    ansB = 0
    for i in range(0, len(S)):
        if ordA[i] != -1:
            ansA += abs(i - ordA[i])
        if ordB[i] != -1:
            ansB += abs(i - ordB[i])
    assert(ansA == ansB)
    return ansA
print(solve(S))