import qualified Data.Set as S
import Data.List
import Data.Bool

nub' = S.toList . S.fromList

main = getContents >>= putStrLn . bool "impossible" "possible" . dave . map read . tail . words

dave :: [Int] -> Bool
dave ws = let s = sum ws in if odd s then False else elem (div s 2) (dp ws)

dp wws@(w:ws) = foldl' (\acc w -> nub' (filter (<=th) ([id, (+w)] <*> acc))) [0,w] ws
 where th = div (sum wws) 2