module Main where
import Control.Monad
import Control.Applicative
import Data.Maybe
import Data.List
import qualified Text.Printf
import qualified Data.ByteString.Char8 as BC
import qualified Data.ByteString as BC

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main :: IO ()
main = do
  n <- readInt
  s <- getLine
  print $ solve s

solve :: String -> Int
solve s = fst $ foldl' f (0, 0) s
  where f (a, b) c
          | c == 'I' = (max a (b+1), b+1)
          | c == 'D' = (max a (b-1), b-1)


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{- Int input -}

parseInt :: BC.ByteString -> Int
parseInt = fst . fromJust . BC.readInt

parseInts :: BC.ByteString -> [Int]
parseInts = map parseInt <$> BC.words

readInt :: IO Int
readInt = parseInt <$> BC.getLine

readInts :: IO [Int]
readInts = parseInts <$> BC.getLine

{- Double Formatting -}

doubleFmt :: Double -> String
doubleFmt = Text.Printf.printf "%.12f"
