import Data.List
import Data.Bool

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

dave :: [Int] -> Bool
dave ws = if odd (sum ws) then False else dave 0 0 ws
 where
  maxw = div (sum ws) 2
  dave l r [] = if l==r then True else False
  dave l r (w:ws)
   | l>maxw || r>maxw = False
   | otherwise = dave (l+w) r ws || dave l (r+w) ws