#include <bits/stdc++.h>

using namespace std;

using int64 = long long;
//const int mod = 1e9 + 7;
const int mod = 998244353;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;


template< typename T1, typename T2 >
ostream &operator<<(ostream &os, const pair< T1, T2 > &p) {
  os << p.first << " " << p.second;
  return os;
}

template< typename T1, typename T2 >
istream &operator>>(istream &is, pair< T1, T2 > &p) {
  is >> p.first >> p.second;
  return is;
}

template< typename T >
ostream &operator<<(ostream &os, const vector< T > &v) {
  for(int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template< typename T >
istream &operator>>(istream &is, vector< T > &v) {
  for(T &in : v) is >> in;
  return is;
}

template< typename T1, typename T2 >
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template< typename T1, typename T2 >
inline bool chmin(T1 &a, T2 b) {
  if(b < 0)b *= -1;
  return a > b && (a = b, true);
}

template< typename T = int64 >
vector< T > make_v(size_t a) {
  return vector< T >(a);
}

template< typename T, typename... Ts >
auto make_v(size_t a, Ts... ts) {
  return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...));
}

template< typename T, typename V >
typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) {
  t = v;
}

template< typename T, typename V >
typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) {
  for(auto &e : t) fill_v(e, v);
}

template< typename F >
struct FixPoint : F {
  FixPoint(F &&f) : F(forward< F >(f)) {}

  template< typename... Args >
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward< Args >(args)...);
  }
};

template< typename F >
inline decltype(auto) MFP(F &&f) {
  return FixPoint< F >{forward< F >(f)};
}

template< typename T = int >
struct Edge {
  int from, to;
  T cost;
  int idx;

  Edge() = default;

  Edge(int from, int to, T cost = 1, int idx = -1) : from(from), to(to), cost(cost), idx(idx) {}

  operator int() const { return to; }
};

template< typename T = int >
struct Graph {
  vector< vector< Edge< T > > > g;
  int es;

  Graph() = default;

  explicit Graph(int n) : g(n), es(0) {}

  size_t size() const {
    return g.size();
  }

  void add_directed_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es++);
  }

  void add_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es);
    g[to].emplace_back(to, from, cost, es++);
  }

  void read(int M, int padding = -1, bool weighted = false, bool directed = false) {
    for(int i = 0; i < M; i++) {
      int a, b;
      cin >> a >> b;
      a += padding;
      b += padding;
      T c = T(1);
      if(weighted) cin >> c;
      if(directed) add_directed_edge(a, b, c);
      else add_edge(a, b, c);
    }
  }
};

template< typename T = int >
using Edges = vector< Edge< T > >;

int main() {
  int N, S, T, K;
  cin >> N >> S >> T >> K;
  --S, --T;
  vector< int > X(N);
  cin >> X;
  int M;
  cin >> M;
  Graph<> g(N);
  g.read(M, -1, true, true);
  auto dp = make_v< int64 >(N, K);
  fill_v(dp, infll);
  vector< vector< pair< int, int > > > pre(N);
  for(int i = 0; i < N; i++) pre[i].assign(K, make_pair(-1, -1));
  dp[S][0] = X[S];
  using pii = tuple< int64, int, int >;
  priority_queue< pii, vector< pii >, greater<> > que;
  que.emplace(dp[S][0], S, 0);
  while(not que.empty()) {
    auto[cost, idx, k]=que.top();
    que.pop();
    if(dp[idx][k] < cost) {
      continue;
    }
    if(idx == T and k + 1 == K) {
      cout << "Possible\n";
      cout << cost << "\n";
      vector< int > ans;
      while(~idx) {
        ans.emplace_back(idx + 1);
        tie(idx, k) = pre[idx][k];
      }
      reverse(begin(ans), end(ans));
      cout << ans.size() << "\n";
      cout << ans << "\n";
      return 0;
    }
    for(auto &to : g.g[idx]) {
      if(chmin(dp[to][min(K - 1, k + 1)], cost + to.cost + X[to])) {
        pre[to][min(K - 1, k + 1)] = {idx, k};
        que.emplace(dp[to][min(K - 1, k + 1)], to, min(K - 1, k + 1));
      }
    }
  }
  cout << "Impossible\n";
}