{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE BinaryLiterals #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE NumDecimals #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}

import Control.Applicative
import Control.Arrow
import Control.Monad
import Control.Monad.ST

import Data.Char
import Data.List
import Data.Maybe

import qualified Data.ByteString.Char8 as B

import Data.Array.ST.Safe
import Data.STRef

import Debug.Trace
import Text.Printf

readInt = readLn :: IO Int
readInts = map ( fst . fromJust . B.readInt ) . B.words <$> B.getLine
readNInts = readInt >>= flip replicateM readInt

which a b f = if f then a else b
mp [ a, b ] = ( a, b )

modifyArray array pos f = writeArray array pos =<< f <$> readArray array pos

main = do
	plusminus <- map ( \c -> if c == 'A' then 1 else -1 ) <$> getLine
	let
		psum = scanl (+) 0 plusminus
	print $ maximum $ map maxdiff $ solve psum

solve psum = runST $ do
	let
		n = succ $ length psum
	occurrences <- newArray ( -n, n ) [] :: ST s ( STArray s Int [Int] )
	forM_ ( zip psum [ 0 .. ] ) $ \( value, pos ) -> 
		modifyArray occurrences value ( pos : )
	getElems occurrences

maxdiff [] = 0
maxdiff as = head as - last as