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)]
  where
    resolve' :: [(Int, [Int])] -> String
    resolve' [] = "impossible"
    resolve' ((a,bs):ps)
      | a == e = "possible"
      | null bs = resolve' ps
      | otherwise = resolve' ((a + (head bs), tail bs):(a, tail bs):ps)