import Control.Applicative
import Data.List

solve :: [Int] -> Bool
solve (w:ws) = iter [w] [] ws where
  iter a b [] = sum a == sum b
  iter a b y@(x:xs)
    | sum a + sum y < sum b || sum a > sum y + sum b = False
    | otherwise  = iter (x:a) b xs || iter a (x:b) xs

main = do
  _ <- getLine
  ws <- fmap (read :: String -> Int) . words <$> getLine
  let a = solve $ ws
  putStrLn $ if a then "possible" else "impossible"