#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <list>
#include <iterator>
#include <cassert>
#include <numeric>
#include <functional>
#include <ctime>
#include <bitset>
#pragma warning(disable:4996) 

//#define ATCODER
#ifdef ATCODER
#include <atcoder/all>
#endif

typedef long long ll;
typedef unsigned long long ull;
#define LINF  9223300000000000000
#define LINF2 1223300000000000000
#define LINF3 1000000000000
#define INF 2140000000
//const long long MOD = 1000000007;
const long long MOD = 998244353;

using namespace std;
#ifdef ATCODER
using namespace atcoder;
#endif

vector<int> pre;

typedef pair<ll, int> P;
vector<ll> dijkstra(int s, const vector<vector<pair<int, int> > >& G) {
    priority_queue< P, vector<P>, greater<P> > que;
    vector<ll> d(G.size(), LINF);
    d[s] = 0;
    que.push(P(0, s));
    while (!que.empty()) {
        int curr = que.top().second;
        ll  dcurr = que.top().first;
        que.pop();
        if (d[curr] < dcurr) continue;
        int i;
        for (i = 0; i < (int)G[curr].size(); i++) {
            int next = G[curr][i].first;
            ll  dist = G[curr][i].second;
            if (d[next] > d[curr] + dist) {
                d[next] = d[curr] + dist;
                que.push(P(d[next], next));
                pre[next] = curr;
            }
        }
    }
    return d;
}

void solve()
{
    int n, S, T, K;
    scanf("%d%d%d%d", &n, &S, &T, &K); S--; T--;
    int num = n * K * 2;
    vector<vector<pair<int, int>>> g(num); 
    pre.resize(num);
#define POS(i,j,k) (((i)*(K)+(j))*2+(k))
    for (int i = 0; i < n; i++) {
        int x;
        scanf("%d", &x);
        for (int j = 0; j < K; j++) {
            g[POS(i, j, 0)].push_back(make_pair(POS(i, j, 1), x));
        }            
    }
    
    int m;
    scanf("%d", &m);
    for (int i = 0; i < m; i++) {
        int a, b, y;
        scanf("%d%d%d", &a, &b, &y); a--; b--;
        for (int j = 0; j < K; j++) {
            g[POS(a, j, 1)].push_back(make_pair(POS(b, min(j+1,K-1), 0), y));
        }
    }
    
    vector<ll> dist = dijkstra(POS(S, 0, 0), g);

    if (dist[POS(T, K-1, 1)] == LINF) {
        printf("Impossible\n");
    }
    else {
        printf("Possible\n%lld\n", dist[POS(T, K-1, 1)]);
        int start = POS(S, 0, 0);
        int curr = POS(T, K - 1, 1);
        vector<int> v;
        while (curr != start) {
            if (curr % 2) v.push_back(curr/2/K);
            curr = pre[curr];
        }
        printf("%d\n", (int)v.size());
        reverse(v.begin(), v.end());
        for (int i = 0; i < (int)v.size(); i++) {
            printf("%d", v[i] + 1);
            if (i < (int)v.size() - 1) printf(" ");
            else printf("\n");
        }
    }

    return;
}

int main()
{
#if 1
    solve();
#else
    int T, t;
    scanf("%d", &T);
    for (t = 0; t < T; t++) {
        //printf("Case #%d: ", t + 1);
        solve();
    }
#endif
    return 0;
}