import qualified Data.Map as M
import qualified Control.Applicative as CA

f :: (Int,Int) -> Char -> (Int,Int)
f (a,p) c
   |c=='A' =(a+1,p+1)
   |otherwise=(a-1,p+1)

toM1 :: (Ord k)=>[(k,Int)]->M.Map k Int
toM1 xs = M.fromListWith up xs
         where up n1 n2=n1

toM2 :: (Ord k)=>[(k,Int)]->M.Map k Int
toM2 xs = M.fromListWith up xs
         where up n1 n2=n2

f2 (Just x)=x
f2 Nothing =0 

main=do
      x<-getLine
      let ys=scanl f (0,0) x
          as=toM1 ys
          bs=toM2 ys
          cs=M.keys as
          ds=map (\x -> (M.lookup x as)) cs
          es=map (\x -> (M.lookup x bs)) cs
          fs=zip ds es
          ans=maximum $ fmap (\(a,b)->CA.liftA2 (-) a b) fs
      print $ f2 $ ans