{-# LANGUAGE BangPatterns #-}
import           Control.Monad.State
import           Data.Bits
import           Data.Bool
import           Data.Char
import           Data.Coerce
import           Data.Word
import qualified Data.ByteString                   as BS
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 l (r + 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.replicate (5001) True
      rep n $ \i -> rev (s `div` 2) (w VU.! i) $ \j -> do
        dpjwi <- VUM.unsafeRead dp (j - w VU.! i)
        VUM.unsafeModify dp (\k -> k .|. dpjwi) j
      putStrLn . bool "impossible" "possible" =<< VUM.unsafeRead dp (s `div` 2)