main :: IO()
main = do
  _ <- getLine 
  str <- getLine
  putStrLn $ solve str

solve :: String -> String
solve str = show.snd $ foldl f (0,0) str
  where
    f :: (Int, Int) -> Char -> (Int, Int)
    f (x,m) 'I' = (x+1, max m (x+1))
    f (x,m) 'D' = (x-1,  m)
    f (x,m) _ = (x,m)
