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

import Data.Bits

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

main' n ws =
    let
        w = map read $ words ws
        s = foldl1 (+) w `div` 2
        a = zip [0..n-1] w
        x = shiftL (1::Int) n
    in
        solve s (x - 1) a

solve _ 0 _ = "impossible"
solve n x a =
    if n == p
        then "posssible"
        else solve n (x - 1) a
    where
        p = foldl (calc x) 0 a
        
calc x p (i,e) = p + if testBit x i then e else 0