-- yukicoder My Practice
-- author: Leonardone @ NEETSDKASU
-- http://yukicoder.me/problems/19

import Data.List

main = do
    n <- getLine
    w <- getLine
    putStrLn $ main' n w

main' n ws =
    let
        w = sort $ map read $ words ws
        s = sum w
        h = s `div` 2
    in
        if h * 2 == s && solve h [0] [] w then "possible" else "impossible"
            

solve _ _ _ [] = False
solve s [] ls (x:xs) = solve s ls [] xs
solve s (t:ts) ls (x:xs)
    | y == s = True
    | y > s = solve s ts ls (x:xs)
    | y < s = solve s ts (y:t:ls) (x:xs)
    where
        y = x + t