#include <bits/stdc++.h>

using namespace std;

typedef long long i64;
typedef unsigned long long ui64;
typedef vector<i64> vi;
typedef vector<vi> vvi;
typedef pair<i64, i64> pi;

#define pb push_back
#define sz(a) i64((a).size())
#define all(c) (c).begin(), (c).end()
#define REP(s, e, i) for(i=(s); i < (e); ++i)
inline void RI(i64 &i) {scanf("%lld", &(i));}
inline void RVI(vi &v) { for(i64 i=0;i<sz(v);++i) { RI(v[i]); } }
inline void RVVI(vvi &vv) { for(i64 i=0;i<sz(vv);++i) { RVI(vv[i]); } }
inline void WI(const i64 &i) {printf("%lld\n", i);}
inline void WVI(const vi &v, char sep=' ') { for(i64 i=0;i<sz(v);++i) { if(i != 0){ printf("%c", sep); } printf("%lld", v[i]);} printf("\n"); }
inline void WS(const string &s) { printf("%s\n", s.c_str()); }
inline void WB(bool b, const string &yes, const string &no) { if(b){ WS(yes);} else { WS(no);} }
inline void YESNO(bool b) { WB(b, "YES", "NO"); }
inline void YesNo(bool b) { WB(b, "Yes", "No"); }
#define BUF_LENGTH 1000000
inline void RS(string &s) {static char buf[BUF_LENGTH]; scanf("%s", buf); s = buf;}
template<typename T> inline bool IN(T &S, const typename T::key_type &key) {
  return S.find(key) != S.end();
}
template<typename T> inline bool ON(const T &b, i64 idx) {
  return ((T(1) << idx) & b) != 0;
}

int main(int argc, char *argv[]) {
  i64 i, j, k;
  i64 N, S, T, K; cin >> N >> S >> T >> K;
  --S; --T; 
  vi X(N); RVI(X);
  vector<vector<pi>> edges(N);
  vector<vector<pi>> r_edges(N);
  i64 M; cin >> M;
  REP(0, M, i) {
    i64 a, b, y; RI(a); RI(b); RI(y); --a; --b; 
    edges[a].pb({b, y});
    r_edges[b].pb({a, y});
  }

  auto update = [](const pi &a, const pi &b) {
    if(b.first == -1) {
      return a;
    }
    if(a.first == -1) {
      return b;
    }
    if(b.first < a.first) {
      return b;
    }
    return a;
  };

  // BFS part
  vector<vector<pi>> TS(K, vector<pi>(N, {-1, -1}));
  TS[0][S] = {X[S], -1};
  REP(0, K-1, k) {
    REP(0, N, i) {
      if(TS[k][i].first >= 0) {
        for(auto &e: edges[i]) {
          i64 n = e.first, w = e.second;
          TS[k+1][n] = update(TS[k+1][n], {TS[k][i].first + w + X[n], i});
        }
      }
    }
  }

  // dijkstra part
  vector<pi> D(N, pi(-1, -1));
  using ppi = pair<pi, i64>;
  priority_queue<ppi, vector<ppi>, greater<ppi>> pq;

  D[T] = {0, -1};
  pq.push({D[T], T});
  while(!pq.empty()) {
    auto c = pq.top(); pq.pop();
    i64 cur = c.second;
    pi d = c.first;
    if(d != D[cur]) {
      continue;
    }
    for(auto &e: r_edges[cur]) {
      i64 n = e.first, w = e.second;
      i64 dn = d.first + X[cur] + w;
      if(D[n].first == -1 || dn < D[n].first) {
        D[n] = {dn, cur};
        pq.push({{dn, cur}, n});
      }
    }
  }

  i64 idx = -1, m = -1;
  REP(0, N, i) {
    if(TS[K-1][i].first != -1 && D[i].first != -1) {
      i64 candidate = TS[K-1][i].first + D[i].first;
      if(m == -1 || candidate < m) {
        m = candidate;
        idx = i;
      }
    }
  }

  if(idx == -1) {
    WS("Impossible");
  }
  else {
    vi ans;
    k = K-1;
    i64 prev = idx;
    while(k >= 0) {
      ans.push_back(prev+1);
      prev = TS[k][prev].second;
      --k;
    }
    reverse(all(ans));
    i64 next = D[idx].second;
    while(next != -1) {
      ans.push_back(next+1);
      next = D[next].second;
    }
    //cerr << idx+1 << endl;
    WS("Possible");
    WI(m);
    WI(sz(ans));
    WVI(ans);
  }

  return 0;
}