import Control.Applicative
import Data.List

func :: [Int] -> [Int]
func [] = [0]
func (x:xs) = nub (sort (map (+ x) t ++ t))
	where
		t = func xs

main = do
	getLine
	a <- map (read::String->Int) . words <$> getLine
	putStrLn $
		if elem ((sum a) `div` 2) (func a)
			then "possible"
			else "impossible"