using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, s, t, k) = (c[0], c[1], c[2], c[3]);
        var x = NList;
        var m = NN;
        var map = NArr(m);
        var tree = new List<(int to, long len)>[n * k];
        var revtree = new List<(int to, long len)>[n * k];
        for (var i = 0; i < tree.Length; ++i)
        {
            tree[i] = new List<(int to, long len)>();
            revtree[i] = new List<(int to, long len)>();
        }
        foreach (var edge in map)
        {
            var a = edge[0] - 1;
            var b = edge[1] - 1;
            for (var i = 0; i + 1 < k; ++i)
            {
                tree[i * n + a].Add(((i + 1) * n + b, x[b] + edge[2]));
                revtree[(i + 1) * n + b].Add((i * n + a, x[b] + edge[2]));
            }
            tree[(k - 1) * n + a].Add(((k - 1) * n + b, x[b] + edge[2]));
            revtree[(k - 1) * n + b].Add(((k - 1) * n + a, x[b] + edge[2]));
        }
        var INF = long.MaxValue / 2;
        var len = Enumerable.Repeat(INF, n * k).ToArray();
        len[s - 1] = x[s - 1];
        var q = new PriorityQueue<Pair>(n, false);
        q.Enqueue(new Pair(s - 1, x[s - 1]));
        while (q.Count > 0)
        {
            var cur = q.Dequeue();
            if (len[cur.Pos] != cur.Val) continue;
            foreach (var next in tree[cur.Pos])
            {
                if (len[next.to] <= cur.Val + next.len) continue;
                len[next.to] = cur.Val + next.len;
                q.Enqueue(new Pair(next.to, len[next.to]));
            }
        }
        if (len[(k - 1) * n + t - 1] == INF)
        {
            WriteLine("Impossible");
        }
        else
        {
            WriteLine("Possible");
            var cur = (k - 1) * n + t - 1;
            var ans = new List<int>();
            while (cur != s - 1)
            {
                ans.Add(cur % n + 1);
                foreach (var next in revtree[cur])
                {
                    if (len[next.to] == len[cur] - next.len)
                    {
                        cur = next.to;
                        break;
                    }
                }
            }
            ans.Add(s);
            ans.Reverse();
            WriteLine(len[(k - 1) * n + t - 1]);
            WriteLine(ans.Count);
            WriteLine(string.Join(" ", ans));
        }
    }
    class Pair : IComparable<Pair>
    {
        public int Pos;
        public long Val;
        public Pair(int pos, long val)
        {
            Pos = pos; Val = val;
        }
        public int CompareTo(Pair b)
        {
            return Val.CompareTo(b.Val);
        }
    }
    class PriorityQueue<T> where T : IComparable<T>
    {
        public T[] List;
        public int Count;
        bool IsTopMax;
        public PriorityQueue(int count, bool isTopMax)
        {
            IsTopMax = isTopMax;
            List = new T[Math.Max(128, count)];
        }
        public void Enqueue(T value)
        {
            if (Count == List.Length)
            {
                var newlist = new T[List.Length * 2];
                for (var i = 0; i < List.Length; ++i) newlist[i] = List[i];
                List = newlist;
            }
            var pos = Count;
            List[pos] = value;
            ++Count;
            while (pos > 0)
            {
                var parent = (pos - 1) / 2;
                if (Calc(List[parent], List[pos], true)) break;
                Swap(parent, pos);
                pos = parent;
            }
        }
        public T Dequeue()
        {
            --Count;
            Swap(0, Count);
            var pos = 0;
            while (true)
            {
                var child = pos * 2 + 1;
                if (child >= Count) break;
                if (child + 1 < Count && Calc(List[child + 1], List[child], false)) ++child;
                if (Calc(List[pos], List[child], true)) break;
                Swap(pos, child);
                pos = child;
            }
            return List[Count];
        }
        bool Calc(T a, T b, bool equalVal)
        {
            var ret = a.CompareTo(b);
            if (ret == 0 && equalVal) return true;
            return IsTopMax ? ret > 0 : ret < 0;
        }
        void Swap(int a, int b)
        {
            var tmp = List[a];
            List[a] = List[b];
            List[b] = tmp;
        }
    }
}