import Data.List
import qualified Data.Set as S
main =
  print . (`div`4) . fst . foldl f (0,S.empty) . drop 1 . words =<< getContents
  where
    f (a,s) c
      | S.member c s = (a+3,S.delete c s)
      | otherwise    = (a+1,S.insert c s)