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

class P
{
    class PriorityQueue<T>
    {
        private readonly List<T> heap;
        private readonly Comparison<T> compare;
        private int size;
        public PriorityQueue() : this(Comparer<T>.Default) { }
        public PriorityQueue(IComparer<T> comparer) : this(16, comparer.Compare) { }
        public PriorityQueue(Comparison<T> comparison) : this(16, comparison) { }
        public PriorityQueue(int capacity, Comparison<T> comparison)
        {
            this.heap = new List<T>(capacity);
            this.compare = comparison;
        }
        public void Enqueue(T item)
        {
            this.heap.Add(item);
            var i = size++;
            while (i > 0)
            {
                var p = (i - 1) >> 1;
                if (compare(this.heap[p], item) <= 0)
                    break;
                this.heap[i] = heap[p];
                i = p;
            }
            this.heap[i] = item;

        }
        public T Dequeue()
        {
            var ret = this.heap[0];
            var x = this.heap[--size];
            var i = 0;
            while ((i << 1) + 1 < size)
            {
                var a = (i << 1) + 1;
                var b = (i << 1) + 2;
                if (b < size && compare(heap[b], heap[a]) < 0) a = b;
                if (compare(heap[a], x) >= 0)
                    break;
                heap[i] = heap[a];
                i = a;
            }
            heap[i] = x;
            heap.RemoveAt(size);
            return ret;
        }
        public T Peek() { return heap[0]; }
        public int Count { get { return size; } }
        public bool Any() { return size > 0; }
    }

    static void Solve()
    {
        while (2 < W.Count)
        {
            int l1 = W.Dequeue();
            int l2 = W.Dequeue();
            W.Enqueue(l1 + l2);
        }
    }

    static int N;
    static PriorityQueue<int> W = new PriorityQueue<int>();

    static void Main(string[] _)
    {
        N = int.Parse(Console.ReadLine());
        _ = Console.ReadLine().Split(' ');
        for (int i = 0; i < N; i++)
        {
            W.Enqueue(int.Parse(_[i]));
        }
        Solve();
        Console.WriteLine(W.Dequeue() == W.Dequeue() ? "possible" : "impossible");
    }
}