import Prelude hiding (lookup)
import Data.Map hiding (map,partition)
import Data.Maybe (fromJust)
type Table = Map (Int,Int) Bool
main = do
  n <- read <$> getLine
  ws <- map read . words <$> getLine
  let
    sumOfWs = sum ws
  putStrLn $ if even sumOfWs && snd (partition empty (n,div sumOfWs 2) ws) then "possible" else "impossible"

partition :: Table -> (Int,Int) -> [Int] -> (Table,Bool)
partition table (n,m) []
  | m == 0 = (table,True)
  | otherwise = (table,False)
partition table (n,m) (w:ws)
  | m < 0 = (table,False)
  | m == 0 = (table,True)
  | otherwise = case lookup (n,m) table of
      Just b -> (table,b)
      Nothing -> (insert (n,m) result table2,result)
      where
        (table1,r1) = partition table (n-1,m) ws
        (table2,r2) = partition table1 (n-1,m-w) ws
        result = r1 || r2