#559 swapAB yukicoder
S=input()
i=0
T=len(S)
r=0
c=0
while i<T and S[i]=="A":
    i+=1
c=i
while i<T and S[i]=="B":
    i+=1
c=i-c
while i<T:
    while i<T and S[i]=="A":
        r+=c
        i+=1
    c=i
    while i<T and S[i]=="B":
        i+=1
    c=i-c
print(r)