import Control.Applicative ((<$>))
import Control.Monad
import Data.List
import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as B8


main :: IO ()
main = do
  getLine
  getl solve >>= print

solve :: ByteString -> Int
solve = length . filter f . group . sort . B8.words
  where
    f x = length x == 1

getl :: (ByteString -> a) -> IO a
getl f = f <$> B8.getLine