#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define drep(i,j,n) for(int i=0;i<(int)(n-1);i++)for(int j=i+1;j<(int)(n);j++)
#define trep(i,j,k,n) for(int i=0;i<(int)(n-2);i++)for(int j=i+1;j<(int)(n-1);j++)for(int k=j+1;k<(int)(n);k++)
#define codefor int test;scanf("%d",&test);while(test--)
#define INT(...) int __VA_ARGS__;in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;in(__VA_ARGS__)
#define yes(ans) if(ans)printf("yes\n");else printf("no\n")
#define Yes(ans) if(ans)printf("Yes\n");else printf("No\n")
#define YES(ans) if(ans)printf("YES\n");else printf("NO\n")
#define popcount(v) __builtin_popcount(v)
#define vector2d(type,name,h,...) vector<vector<type>>name(h,vector<type>(__VA_ARGS__))
#define vector3d(type,name,h,w,...) vector<vector<vector<type>>>name(h,vector<vector<type>>(w,vector<type>(__VA_ARGS__)))
#define umap unordered_map
#define uset unordered_set
using namespace std;
using ll = long long;
const int MOD=1000000007;
const int MOD2=998244353;
const int INF=1<<30;
const ll INF2=1LL<<60;
//入力系
void scan(int& a){scanf("%d",&a);}
void scan(long long& a){scanf("%lld",&a);}
template<class T,class L>void scan(pair<T, L>& p){scan(p.first);scan(p.second);}
template<class T,class U,class V>void scan(tuple<T,U,V>& p){scan(get<0>(p));scan(get<1>(p));scan(get<2>(p));}
template<class T> void scan(T& a){cin>>a;}
template<class T> void scan(vector<T>& vec){for(auto&& it:vec)scan(it);}
void in(){}
template <class Head, class... Tail> void in(Head& head, Tail&... tail){scan(head);in(tail...);}
//出力系
void print(const int& a){printf("%d",a);}
void print(const long long& a){printf("%lld",a);}
void print(const double& a){printf("%.15lf",a);}
template<class T,class L>void print(const pair<T, L>& p){print(p.first);putchar(' ');print(p.second);}
template<class T> void print(const T& a){cout<<a;}
template<class T> void print(const vector<T>& vec){if(vec.empty())return;print(vec[0]);for(auto it=vec.begin();++it!= vec.end();){putchar(' ');print(*it);}}
void out(){putchar('\n');}
template<class T> void out(const T& t){print(t);putchar('\n');}
template <class Head, class... Tail> void out(const Head& head,const Tail&... tail){print(head);putchar(' ');out(tail...);}
//デバッグ系
template<class T> void dprint(const T& a){cerr<<a;}
template<class T> void dprint(const vector<T>& vec){if(vec.empty())return;cerr<<vec[0];for(auto it=vec.begin();++it!= vec.end();){cerr<<" "<<*it;}}
void debug(){cerr<<endl;}
template<class T> void debug(const T& t){dprint(t);cerr<<endl;}
template <class Head, class... Tail> void debug(const Head& head, const Tail&... tail){dprint(head);cerr<<" ";debug(tail...);}
ll intpow(ll a, ll b){ ll ans = 1; while(b){ if(b & 1) ans *= a; a *= a; b /= 2; } return ans; }
ll modpow(ll a, ll b, ll p){ ll ans = 1; while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; }
ll modinv(ll a, ll m) {ll b = m, u = 1, v = 0;while (b) {ll t = a / b;a -= t * b; swap(a, b);u -= t * v; swap(u, v);}u %= m;if (u < 0) u += m;return u;}
ll updivide(ll a,ll b){return (a+b-1)/b;}
template<class T> void chmax(T &a,const T b){if(b>a)a=b;}
template<class T> void chmin(T &a,const T b){if(b<a)a=b;}

int maxv;
ll rec(int v,int t,int i,int k,vector<ll> &x,vector<vector<pair<int,int>>> &g,vector<vector<ll>> &dp){
    if(i>=k-1&&v==t){
        return dp[v][i]=x[v];
    }
    if(i+1>=maxv)return dp[v][i]=(1LL<<59);
    if(dp[v][i]!=-1)return dp[v][i];
    dp[v][i]=(1LL<<59);
    int u,w;
    rep(j,g[v].size()){
        tie(u,w)=g[v][j];
        chmin(dp[v][i],x[v]+w+rec(u,t,i+1,k,x,g,dp));
    }
    return dp[v][i];
}

ll target;
vector<int> order;
bool rec2(int v,int t,int i,int k,ll value,vector<ll> &x,
        vector<vector<pair<int,int>>> &g,vector<vector<ll>> &dp,vector<vector<bool>> &dp2){
    if(i>=k-1&&v==t&&value==x[v]){
        order.push_back(v+1);
        out(order.size());
        out(order);
        return 1;
    }
    if(i+1>=maxv)return false;
    if(dp2[v][i])return false;
    int u,w;
    order.push_back(v+1);
    rep(j,g[v].size()){
        tie(u,w)=g[v][j];
        if(value-(x[v]+w)==dp[u][i+1]){
            if(rec2(u,t,i+1,k,dp[u][i+1],x,g,dp,dp2))return true;
        }
    }
    order.pop_back();
    dp[v][i]=true;
    return false;
}

int main(){
    INT(n,s,t,k);
    s--,t--;
    vector<ll> x(n);
    vector<vector<pair<int,int>>> g(n);
    in(x);
    INT(m);
    int u,v,w;
    rep(i,m){
        in(u,v,w);
        g[--u].emplace_back(--v,w);
    }
    if(k>=1000){
        maxv=10*k;
        vector2d(ll,dp,n,maxv,-1);
        vector2d(bool,dp2,n,maxv,false);
        ll ans=rec(s,t,0,k,x,g,dp);
        if(ans>=(1LL<<59)){
            out("Impossible");
            return 0;
        }
        out("Possible");
        out(ans);
        rec2(s,t,0,k,ans,x,g,dp,dp2);
    }else if(n>=1000){
        maxv=10*k;
        for(int i=1;i<=100;i++){
            if(i*k*n<=100000000){
                maxv=i*k;
            }else break;
        }
        vector2d(ll,dp,n,maxv,-1);
        vector2d(bool,dp2,n,maxv,false);
        ll ans=rec(s,t,0,k,x,g,dp);
        if(ans>=(1LL<<59)){
            out("Impossible");
            return 0;
        }
        out("Possible");
        out(ans);
        rec2(s,t,0,k,ans,x,g,dp,dp2);
    }else{
        maxv=100*k;
        vector2d(ll,dp,n,maxv,-1);
        vector2d(bool,dp2,n,maxv,false);
        ll ans=rec(s,t,0,k,x,g,dp);
        if(ans>=(1LL<<59)){
            out("Impossible");
            return 0;
        }
        out("Possible");
        out(ans);
        rec2(s,t,0,k,ans,x,g,dp,dp2);
    }
}