#pragma GCC optimize("O3")
#include<bits/stdc++.h> 
using namespace std;
using ll=long long;
using P=pair<ll,ll>;
template<class T> using V=vector<T>; 
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
const ll inf=(1e18);
//const ll mod=998244353;
const ll mod=1000000007;
ll GCD(ll a,ll b) {return b ? GCD(b,a%b):a;}
ll LCM(ll c,ll d){return c/GCD(c,d)*d;}
struct __INIT{__INIT(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);}} __init;
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T>void debag(const vector<T> &a){cerr<<"debag :";for(auto v:a)cerr<<v<<" ";cerr<<"\n";}
template<class T>void print(const vector<T> &a){for(auto v:a)cout<<v<<" ";cout<<"\n";}
using tp=tuple<ll,int,int>;
int main(){
     int n,s,t,k;
     cin>>n>>s>>t>>k;
     s--;t--;
     V<ll> x(n);
     for(int i=0;i<n;i++)cin>>x[i];
     V<V<P>> dp(k+1,V<P>(n+5,P{inf,inf}));
     ll m;
     cin>>m;
     V<V<P>> g(n);
     map<P,ll> mp;
     for(int i=0;i<m;i++){
           ll a,b,c;
           cin>>a>>b>>c;
           --a;--b;
           g[a].emplace_back(b,c);
           mp[{a,b}]=c;
     }
     dp[1][s]=P(x[s],-1);
     priority_queue<tp,V<tp>,greater<tp>> pq;
     pq.emplace(dp[1][s].fi,1,s);
     while(pq.size()){
            auto [v,tim,cur]=pq.top();
            pq.pop();
            if(dp[tim][cur].fi<v)continue;
            for(auto &[to,cost]:g[cur]){
                      P nxt={cost+x[to]+v,cur};
                      if(chmin(dp[min(k,tim+1)][to],nxt)){
                             pq.emplace(nxt.fi,min(k,tim+1),to);
                      }
            }
    }
     if(dp[k][t].fi>=inf){
         cout<<"Impossible"<<"\n";
         return 0;
     }
     int cur=t,id=k;
     V<int> ans;
     while(cur!=-1){
           ans.emplace_back(cur+1);
           int bfo=cur;
           cur=dp[id][cur].se;
           if(cur==-1)break;
           if(id!=k||dp[id][bfo].fi!=dp[id][cur].fi+x[bfo]+mp[{cur,bfo}]){
           id--;
           }
     }
     cout<<"Possible"<<"\n";
     cout<<dp[k][t].fi<<"\n";
     cout<<ans.size()<<"\n";
     reverse(all(ans));
     print(ans);
}