import Data.List

main = do
  n <- readLn :: IO Int
  ws <- (map read . words) <$> getLine
  putStrLn $ if odd (sum ws) then "impossible" else resolve ws

resolve ws = resolve' (powerset (reverse (takeWhile (< wt) $ sort ws))) wt
  where
    wt = (sum ws) `div` 2
    resolve' [] _ = "impossible"
    resolve' (x:xs) a
      | sum x == a = "possible"
      | otherwise = resolve' xs a

powerset [] = [[]]
powerset (x:xs) = [x:ps | ps <- powerset xs] ++ powerset xs