import Data.List

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 then "impossible" else resolve e ws'

resolve e ws = resolve' [0] ws
  where
    resolve' :: [Int] -> [Int] -> String
    resolve' r [] = if e `elem` r then "possible" else "impossible"
    resolve' r (x:xs) = resolve' (union r (map (+ x) r)) xs