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) ws where 
  total = sum ws

make 0 _ = True
make n [] = False
make n (w:ws)
  | n < 0 = False
  | n == w = True
  | n < w  = make n ws
  | True   = make (n-w) ws || make n ws