import Control.Applicative
import Data.List
import Data.IntMap (IntMap, (!))
import qualified Data.IntMap as IM

main :: IO ()
main = solve <$> getLine >>= print

solve :: String -> Int
solve = (\(_, _, x, _) -> x) . foldl' f (1, IM.insert 0 0 IM.empty, 0, 0)
  where
    f (i, mp, mx, d) c
      | IM.member nd mp = (i+1, mp, max mx (i - mp ! nd), nd)
      | otherwise = (i+1, IM.insert nd i mp, mx, nd)
      where
        nd = if c == 'A' then d+1 else d-1