let ``No.4 おもりと天秤`` () =
    let c = int(stdin.ReadLine()) - 1
    let l =
        stdin.ReadLine().Split(' ')
        |> Seq.map int
        |> Seq.toList
    let m = List.sum l
    let p =
        if m &&& 1 = 1 then 0
        else
            let m2 = m/2
            let dp = Array.init 10000 (fun _ -> 0)
            dp.[0] <- 1
            for i in 0..c do
                for j in (seq[m2..(-1)..(l.[i])]) do
                    dp.[j] <- (dp.[j] ||| dp.[j-l.[i]])
            dp.[m2]
    printfn "%s" ["impossible";"possible";].[p]
``No.4 おもりと天秤`` ()