#include <bits/stdc++.h>
using namespace std;
const long long INF = 1000000000000000;
int main(){
  int N, S, T, K;
  cin >> N >> S >> T >> K;
  S--;
  T--;
  vector<int> X(N);
  for (int i = 0; i < N; i++){
    cin >> X[i];
  }
  int M;
  cin >> M;
  vector<vector<pair<int, int>>> E(N), E2(N);
  for (int i = 0; i < M; i++){
    int A, B, Y;
    cin >> A >> B >> Y;
    A--;
    B--;
    E[A].push_back(make_pair(Y, B));
    E2[B].push_back(make_pair(Y, A));
  }
  vector<vector<long long>> dp(K, vector<long long>(N, INF));
  vector<vector<int>> pr1(K, vector<int>(N, -1));
  dp[0][S] = X[S];
  for (int i = 0; i < K - 1; i++){
    for (int j = 0; j < N; j++){
      for (auto P : E[j]){
        int w = P.second;
        long long sum = dp[i][j] + P.first + X[w];
        if (dp[i + 1][w] > sum){
          pr1[i + 1][w] = j;
          dp[i + 1][w] = sum;
        }
      }
    }
  }
  vector<long long> d(N, INF);
  vector<int> pr2(N);
  priority_queue<tuple<long long, int, int>, vector<tuple<long long, int, int>>, greater<tuple<long long, int, int>>> pq;
  pq.push(make_tuple(0, T, -1));
  while (!pq.empty()){
    long long dd = get<0>(pq.top());
    int v = get<1>(pq.top());
    int p = get<2>(pq.top());
    pq.pop();
    if (d[v] == INF){
      d[v] = dd;
      pr2[v] = p;
      for (auto P : E2[v]){
        int w = P.second;
        if (d[w] == INF){
          pq.push(make_tuple(dd + X[v] + P.first, w, v));
        }
      }
    }
  }
  long long mn = INF, t = -1;
  for (int i = 0; i < N; i++){
    long long sum = dp[K - 1][i] + d[i];
    if (sum < mn){
      mn = sum;
      t = i;
    }
  }
  if (t == -1){
    cout << "Impossible" << endl;
  } else {
    vector<int> ans;
    int t1 = t;
    ans.push_back(t1);
    for (int i = K - 1; i >= 1; i--){
      int tmp = pr1[i][t1];
      ans.push_back(tmp);
      t1 = tmp;
    }
    reverse(ans.begin(), ans.end());
    int t2 = t;
    while (t2 != T){
      t2 = pr2[t2];
      ans.push_back(t2);
    }
    cout << "Possible" << endl;
    cout << mn << endl;
    int R = ans.size();
    cout << R << endl;
    for (int i = 0; i < R; i++){
      cout << ans[i] + 1;
      if (i < R - 1){
        cout << ' ';
      }
    }
    cout << endl;
  }
}