import Data.Set (Set, (\\))
import Data.Set qualified as S

closure :: Ord a => (a -> a) -> Set a -> Set a
closure f s = go S.empty s
 where
  go old new | null new  = old
             | otherwise = go old' new'
   where
    old' = old <> new
    new' = S.map f new \\ old'
    

main :: IO ()
main = print $ closure (`div` 2) (S.singleton 512)