import Data.List

main = do
  getLine
  l <- getLine
  let ws = map read $ words l
  let r = compute ws
  putStrLn $ if r then "possible" else "impossible"

compute ws = even total && elem (div total 2) (make ws) where
  total = sum ws

make [] = [0]
make (x:xs) = ws ++ map (x+) ws where ws = make xs