#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

template <class T, class U>
vector<T> make_v(U size, const T& init){ return vector<T>(static_cast<size_t>(size), init); }

template<class... Ts, class U>
auto make_v(U size, Ts... rest) { return vector<decltype(make_v(rest...))>(static_cast<size_t>(size), make_v(rest...)); }

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template <class K, class V>
class RadixHeap {
    static constexpr int bit_length = sizeof(K)*8;
    K last;
    size_t sz, cnt;
    array<vector<pair<K, V>>, bit_length> v;
    static inline int bsr(int x){
        return x ? bit_length-__builtin_clz(x) : 0;
    }
    static inline int bsr(ll x){
        return x ? bit_length-__builtin_clzll(x) : 0;
    }

    void pull() {
        if(cnt < v[0].size()) return;;
        int i = 1;
        while(v[i].empty()) i++;
        last = min_element(v[i].begin(),v[i].end())->first;
        for (auto &&x : v[i]) v[bsr(x.first ^ last)].push_back(x);
        v[i].clear();
    }
public:
    RadixHeap() : last(0), sz(0), cnt(0) {}
    void emplace(K x, V val){
        sz++;
        v[bsr(x^last)].emplace_back(x, val);
    }

    pair<K, V> top() {
        pull();
        return v[0][cnt];
    }

    void pop() {
        pull();
        sz--;
        cnt++;
    }

    size_t size() const { return sz; }
    bool empty() const { return !sz; }
};

int main() {
    int n, s, t, k;
    cin >> n >> s >> t >> k;
    s--; t--;
    vector<int> X(n);
    for (auto &&i : X) scanf("%d", &i);
    vector<vector<pair<int, int>>> G(n);
    int m;
    cin >> m;
    for (int i = 0; i < m; ++i) {
        int a, b, y;
        scanf("%d %d %d", &a, &b, &y);
        a-- ;b--;
        G[a].emplace_back(b, X[b]+y);
    }
    auto dp = make_v(k+1, n, INF<ll>);
    auto prv = make_v(k+1, n, pair<int, int>(-1, -1));
    dp[1][s] = X[s];
    for (int i = 1; i < k; ++i) {
        for (int j = 0; j < n; ++j) {
            for (auto [l, v] : G[j]) {
                if(chmin(dp[i+1][l], dp[i][j]+v)){
                    prv[i+1][l] = {i, j};
                }
            }
        }
    }
    RadixHeap<ll, int> Q;
    for (int i = 0; i < n; ++i) {
        Q.emplace(dp[k][i], i);
    }
    while(!Q.empty()){
        auto [val, x] = Q.top(); Q.pop();
        if(dp[k][x] < val) continue;
        for (auto [l, v] : G[x]) {
            if(dp[k][l] > val+v){
                dp[k][l] = val+v;
                Q.emplace(val+v, l);
                prv[k][l] = {k, x};
            }
        }
    }
    if(dp[k][t] == INF<ll>) {
        puts("Impossible");
    }else {
        puts("Possible");
        cout << dp[k][t] << "\n";
        ll p = k, q = t;
        vector<ll> ans;
        while(prv[p][q].first > 0){
            ans.emplace_back(q);
            tie(p, q) = prv[p][q];
        }
        ans.emplace_back(q);
        reverse(ans.begin(),ans.end());
        cout << ans.size() << "\n";
        for (int i = 0; i < ans.size(); ++i) {
            if(i) printf(" ");
            printf("%lld", ans[i]+1);
        }
        puts("");
    }
    return 0;
}