{-# LANGUAGE BangPatterns #-}
import           Control.Monad.State
import           Data.Bool
import           Data.Char
import           Data.Coerce
import qualified Data.ByteString.Char8             as BSC8
import qualified Data.Vector.Fusion.Stream.Monadic as VFSM
import qualified Data.Vector.Unboxed               as VU
import qualified Data.Vector.Unboxed.Mutable       as VUM
type Parser a = StateT BSC8.ByteString Maybe a
runParser :: Parser a -> BSC8.ByteString -> Maybe (a, BSC8.ByteString)
runParser = runStateT
{-# INLINE runParser #-}
int :: Parser Int
int = coerce $ BSC8.readInt . BSC8.dropWhile isSpace
{-# INLINE int #-}
seqInput :: Int -> IO (VU.Vector Int)
seqInput n = VU.unfoldrN n (runParser int) <$> BSC8.getLine
stream :: Monad m => Int -> Int -> VFSM.Stream m Int
stream !l !r = VFSM.Stream step l
  where
    step x
      | x < r     = return $ VFSM.Yield x (x + 1)
      | otherwise = return $ VFSM.Done
    {-# INLINE [0] step #-}
{-# INLINE [1] stream #-}
rep :: Monad m => Int -> (Int -> m ()) -> m ()
rep n = flip VFSM.mapM_ (stream 0 n)
{-# INLINE rep #-}
streamR :: Monad m => Int -> Int -> VFSM.Stream m Int
streamR !l !r = VFSM.Stream step (r - 1)
  where
    step x
      | x >= l    = return $ VFSM.Yield x (x - 1)
      | otherwise = return $ VFSM.Done
    {-# INLINE [0] step #-}
{-# INLINE [1] streamR #-}
rev :: Monad m => Int -> Int -> (Int -> m ()) -> m ()
rev l r = flip VFSM.mapM_ (streamR r (l + 1))
{-# INLINE rev #-}
main :: IO ()
main = do
  n <- readLn :: IO Int
  w <- seqInput n
  let s = VU.sum w
  if odd s
    then putStrLn "impossible"
    else do
      dp <- VUM.unsafeNew 10001
      VUM.unsafeWrite dp 0 (True :: Bool)
      rep n $ \i -> rev (div s 2) (w VU.! i) $ \j -> do
        item <- VUM.unsafeRead dp (j - w VU.! i)
        VUM.unsafeModify dp (|| item) j
      b <- VUM.unsafeRead dp (div s 2)
      putStrLn $ bool "impossible" "possible" b