/* -*- coding: utf-8 -*-
 *
 * 1545.cc:  No.1545 [Cherry 2nd Tune N] Anthem - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;
const int MAX_K = 30000;

/* typedef */

typedef unsigned int ui;
typedef vector<ui> vu;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ui> plu;
typedef vector<pii> vpii;
typedef map<ui,ll> mul;
typedef map<ui,ui> muu;

/* global variables */

int xs[MAX_N];
vpii nbrs[MAX_N];
mul ds;
muu ps;

/* subroutines */

inline ui ab2p(ui a, ui b, int k) { return a * k + b; }
inline void p2ab(ui p, ui &a, ui &b, int k) { a = p / k, b = p % k; }

/* main */

int main() {
  int n, st, gl, k;
  scanf("%d%d%d%d", &n, &st, &gl, &k);
  st--, gl--;

  for (int i = 0; i < n; i++) scanf("%d", xs + i);

  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--;
    nbrs[a].push_back(pii(b, y));
  }

  ui stp = ab2p(st, 0, k), glp = ab2p(gl, k - 1, k);

  ds[stp] = xs[st];

  priority_queue<plu> q;
  q.push(plu(-xs[st], stp));

  while (! q.empty()) {
    plu u = q.top(); q.pop();
    ll ud = -u.first;
    ui up = u.second;
    if (ds[up] != ud) continue;
    if (up == glp) break;

    ui ua, ub;
    p2ab(up, ua, ub, k);

    for (auto vy: nbrs[ua]) {
      ui va = vy.first, vb = min<ui>(ub + 1, k - 1);
      ui vp = ab2p(va, vb, k);
      ll vd = ud + vy.second + xs[va];
      mul::iterator mit = ds.find(vp);
      if (mit == ds.end()) {
	ds[vp] = vd;
	ps[vp] = up;
	q.push(plu(-vd, vp));
      }
      else if (mit->second > vd) {
	mit->second = vd;
	ps[vp] = up;
	q.push(plu(-vd, vp));
      }
    }
  }

  mul::iterator mit = ds.find(glp);
  if (mit == ds.end()) puts("Impossible");
  else {
    vu vs;
    vs.push_back(gl);
    for (muu::iterator mit0 = ps.find(glp); mit0 != ps.end();) {
      vs.push_back(mit0->second / k);
      mit0 = ps.find(mit0->second);
    }

    printf("Possible\n%lld\n%lu\n", mit->second, vs.size());
    for (int i = vs.size() - 1; i >= 0; i--)
      printf("%u%c", vs[i] + 1, (i > 0) ? ' ' : '\n');
  }
  return 0;
}