main = do
  n <- readLn :: IO Int
  ws <- (map read . words) <$> getLine
  let e = (sum ws) `div` 2
  let ws' = filter (<= e) ws
  putStrLn $ if (odd $ sum ws) || (sum ws' < e) then "impossible" else resolve e ws'

resolve e ws = resolve' 0 ws ws
  where
    resolve' :: Int -> [Int] -> [Int] -> String
    resolve' _ [] [] = "impossible"
    resolve' _ [] (p:ps) = resolve' 0 ps ps
    resolve' s (q:qs) ps
      | s == e = "possible"
      | null qs = if s + q == e then "possible" else resolve' s qs ps
      | otherwise = resolve' (s+q) qs ps