s,counter=list(map(int,input().replace("A","1").replace("B","2"))),0
OK=sorted(s)
while OK!=s:
    for i in range(len(s)-1):
        if s[i]>s[i+1]:
            t=s[i]
            s[i]=s[i+1]
            s[i+1]=t
            counter+=1
print(counter)