using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static string InputPattern = "Input4";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("3");
            WillReturn.Add("1 2 3");
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("5");
            WillReturn.Add("1 2 3 4 5");
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("15");
            WillReturn.Add("62 8 90 2 24 62 38 64 76 60 30 76 80 74 72");
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    struct JyoutaiDef
    {
        internal int CurrP;
        internal HashSet<int> SelectedLeftOmoriIndSet;
        internal HashSet<int> SelectedRightOmoriIndSet;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();

        int[] OmoriArr =
            InputList.Skip(1).SelectMany(X => X.Split(' '), (X, Y) => int.Parse(Y)).ToArray();

        //事前に総和の半分を求めておく
        int OmoriSum = OmoriArr.Sum();

        //総和が奇数ならその時点で解なしとなる
        if (OmoriSum % 2 == 1) {
            Console.WriteLine("impossible");
            return;
        }

        var stk = new Stack<JyoutaiDef>();
        JyoutaiDef WillPush;
        WillPush.CurrP = 0;
        WillPush.SelectedLeftOmoriIndSet = new HashSet<int>() { 0 }; //1つめの重りは必ず左にセット
        WillPush.SelectedRightOmoriIndSet = new HashSet<int>();
        stk.Push(WillPush);

        while (stk.Count > 0) {
            JyoutaiDef Popped = stk.Pop();

            //クリア判定
            int LeftSum; int pRightSum;
            DeriveOmoriSumArr(OmoriArr,
                              Popped.SelectedLeftOmoriIndSet,
                              Popped.SelectedRightOmoriIndSet,
                              out LeftSum, out pRightSum);

            if (LeftSum == OmoriSum / 2) {
                Console.WriteLine("possible");
                return;
            }
            else if (LeftSum > OmoriSum / 2) continue; //総和の半分を超えたら枝切り
            else if (pRightSum > OmoriSum / 2) continue; //総和の半分を超えたら枝切り

            if (Popped.CurrP > OmoriArr.GetUpperBound(0)) continue;

            //重りを左にセットする経路のPush
            WillPush.CurrP = Popped.CurrP + 1;
            WillPush.SelectedLeftOmoriIndSet = new HashSet<int>(Popped.SelectedLeftOmoriIndSet) { WillPush.CurrP };
            WillPush.SelectedRightOmoriIndSet = Popped.SelectedRightOmoriIndSet;
            stk.Push(WillPush);

            //重りを右にセットする経路のPush
            WillPush.SelectedLeftOmoriIndSet = Popped.SelectedRightOmoriIndSet;
            WillPush.SelectedRightOmoriIndSet = new HashSet<int>(Popped.SelectedRightOmoriIndSet) { WillPush.CurrP };
            stk.Push(WillPush);
        }
        Console.WriteLine("impossible");
    }

    //重りの添字Listを引数として、2つの天秤の重りの合計を求める
    static void DeriveOmoriSumArr(int[] pOmoriArr,
                                  HashSet<int> pSelectedLeftOmoriIndSet,
                                  HashSet<int> pSelectedRightOmoriIndSet,
                                  out int pLeftSum, out int pRightSum)
    {
        pLeftSum = pRightSum = 0;
        for (int I = 0; I <= pOmoriArr.GetUpperBound(0); I++) {
            if (pSelectedLeftOmoriIndSet.Contains(I)) {
                pLeftSum += pOmoriArr[I];
            }
            if (pSelectedRightOmoriIndSet.Contains(I)) {
                pRightSum += pOmoriArr[I];
            }
        }
    }
}