#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
// #include<ext/pb_ds/tag_and_trait.hpp>
// using namespace __gnu_pbds;
// #include<boost/multiprecision/cpp_int.hpp>
// namespace multiprecisioninteger = boost::multiprecision;
// using cint=multiprecisioninteger::cpp_int;
using namespace std;
using ll=long long;
using datas=pair<ll,ll>;
using ddatas=pair<long double,long double>;
using tdata=pair<ll,datas>;
using vec=vector<ll>;
using mat=vector<vec>;
using pvec=vector<datas>;
using pmat=vector<pvec>;
// using llset=tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>;
#define For(i,a,b) for(i=a;i<(ll)b;++i)
#define bFor(i,b,a) for(i=b,--i;i>=(ll)a;--i)
#define rep(i,N) For(i,0,N)
#define rep1(i,N) For(i,1,N)
#define brep(i,N) bFor(i,N,0)
#define brep1(i,N) bFor(i,N,1)
#define all(v) (v).begin(),(v).end()
#define allr(v) (v).rbegin(),(v).rend()
#define vsort(v) sort(all(v))
#define vrsort(v) sort(allr(v))
#define uniq(v) vsort(v);(v).erase(unique(all(v)),(v).end())
#define endl "\n"
#define popcount __builtin_popcountll
#define eb emplace_back
#define print(x) cout<<x<<endl
#define printyes print("Yes")
#define printno print("No")
#define printYES print("YES")
#define printNO print("NO")
#define output(v) do{bool f=0;for(auto outi:v){cout<<(f?" ":"")<<outi;f=1;}cout<<endl;}while(0)
#define matoutput(v) do{for(auto outimat:v)output(outimat);}while(0)
constexpr ll mod=1000000007;
// constexpr ll mod=998244353;
constexpr ll inf=1LL<<60;
constexpr long double eps=1e-9;
const long double PI=acosl(-1);
template<class T,class E> ostream& operator<<(ostream& os,const pair<T,E>& p){return os<<"("<<p.first<<","<<p.second<<")";}
template<class T> ostream& operator<<(ostream& os,const vector<T>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T> ostream& operator<<(ostream& os,const set<T>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T> ostream& operator<<(ostream& os,const multiset<T>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T,class E> ostream& operator<<(ostream& os,const map<T,E>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T> inline bool chmax(T& a,const T b){bool x=a<b;if(x)a=b;return x;}
template<class T> inline bool chmin(T& a,const T b){bool x=a>b;if(x)a=b;return x;}
#ifdef DEBUG
void debugg(){cout<<endl;}
template<class T,class... Args>void debugg(const T& x,const Args&... args){cout<<" "<<x;debugg(args...);}
#define debug(...) cout<<__LINE__<<" ["<<#__VA_ARGS__<<"]:",debugg(__VA_ARGS__)
#else
#define debug(...) (void(0))
#endif

inline void startupcpp(void) noexcept{
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout<<fixed<<setprecision(15);
}
vector<ll> dijkstra(pmat& g,ll first){
  priority_queue<datas,pvec,greater<datas>> que;
  que.emplace(0,first);
  vector<ll> dist(g.size(),inf);
  while(!que.empty()){
    datas x=que.top();que.pop();
    if(!chmin(dist[x.second],x.first))continue;
    for(auto next:g[x.second]){
      next.first+=x.first;
      if(!chmin(dist[next.second],next.first+1))continue;
      que.emplace(next);
    }
  }
  return dist;
}

ll N,M,K,H,W,A,B,C,D;
int main(){
  startupcpp();
  // int codeforces;cin>>codeforces;while(codeforces--){
  ll i,j;
  cin>>N>>A>>B>>K;
  --A;--B;
  vec x(N);
  rep(i,N){
    cin>>x[i];
    x[i]*=2;
  }
  cin>>M;
  pmat g(N),rg(N);
  rep(i,M){
    ll a,b,c;
    cin>>a>>b>>c;
    c*=2;
    --a;--b;
    g[a].emplace_back(c+(x[a]+x[b])/2,b);
    rg[b].emplace_back(c+(x[a]+x[b])/2,a);
  }
  mat dp(K,vec(N,inf)),bf(K,vec(N));
  dp[0][A]=x[A]/2;
  rep(i,K-1){
    rep(j,N){
      for(auto [d,to]:g[j]){
        if(chmin(dp[i+1][to],dp[i][j]+d))bf[i+1][to]=j;
      }
    }
  }
  auto dist=dijkstra(rg,B);
  vec anslist(N);
  rep(i,N)anslist[i]=dist[i]+dp[K-1][i];
  i=min_element(all(anslist))-anslist.begin();
  if(anslist[i]>=inf){
    print("Impossible");
    return 0;
  }
  print("Possible");
  assert((anslist[i]+x[B]/2)%2==0);
  print((anslist[i]+x[B]/2)/2);
  vec ans(K);
  ans[K-1]=i;
  rep1(j,K)ans[j-1]=bf[j][ans[j]];
  while(ans.back()!=B){
    for(auto [d,x]:g[ans.back()]){
      if(dist[ans.back()]==dist[x]+d){
        ans.emplace_back(x);
        break;
      }
    }
  }
  print(ans.size());
  for(auto& x:ans)++x;
  output(ans);
// }
}