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 && make (div total 2) (zip ws1 ss) where
  total = sum ws
  ws1 = sortBy (flip compare) ws
  ss = scanr (+) 0 ws1

make n [] = n == 0
make n ((w,s):wss)
 | n > s = False
 | n < 0 = False
 | n ==0 = True
 | n < w = make n wss
 | True  = make (n-w) wss || make n wss