import Data.List

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

resolve ws = resolve' (getPairs n' 0 ws)
  where
    n' = (sum ws) `div` 2
    resolve' :: [(Int, [Int])] -> String
    resolve' [] = "impossible"
    resolve' pairs@((a,bs):ps)
      | a == n' = "possible"
      | null bs = resolve' ps
      | otherwise = resolve' (getPairs n' a bs)

getPairs :: Int -> Int -> [Int] -> [(Int,[Int])]
getPairs e c (p:ps)
  | null ps = [(m, [])]
  | otherwise = (m, filter (<= (e - m)) ps):(getPairs e c ps)
    where m = c + p