#define LOCAL
#include <bits/stdc++.h>
using namespace std;
#pragma region Macros
typedef long long ll;
typedef __int128_t i128;
typedef unsigned int uint;
typedef unsigned long long ull;
#define ALL(x) (x).begin(), (x).end()

template <typename T> istream& operator>>(istream& is, vector<T>& v) {
    for (T& x : v) is >> x;
    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 == (int)v.size() ? "" : " ");
    }
    return os;
}
template <typename T, typename U> ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <typename T, typename U, typename V> ostream& operator<<(ostream& os, const tuple<T, U, V>& t) {
    os << '(' << get<0>(t) << ',' << get<1>(t) << ',' << get<2>(t) << ')';
    return os;
}
template <typename T, typename U, typename V, typename W> ostream& operator<<(ostream& os, const tuple<T, U, V, W>& t) {
    os << '(' << get<0>(t) << ',' << get<1>(t) << ',' << get<2>(t) << ',' << get<3>(t) << ')';
    return os;
}
template <typename T, typename U> ostream& operator<<(ostream& os, const map<T, U>& m) {
    os << '{';
    for (auto itr = m.begin(); itr != m.end();) {
        os << '(' << itr->first << ',' << itr->second << ')';
        if (++itr != m.end()) os << ',';
    }
    os << '}';
    return os;
}
template <typename T, typename U> ostream& operator<<(ostream& os, const unordered_map<T, U>& m) {
    os << '{';
    for (auto itr = m.begin(); itr != m.end();) {
        os << '(' << itr->first << ',' << itr->second << ')';
        if (++itr != m.end()) os << ',';
    }
    os << '}';
    return os;
}
template <typename T> ostream& operator<<(ostream& os, const set<T>& s) {
    os << '{';
    for (auto itr = s.begin(); itr != s.end();) {
        os << *itr;
        if (++itr != s.end()) os << ',';
    }
    os << '}';
    return os;
}
template <typename T> ostream& operator<<(ostream& os, const multiset<T>& s) {
    os << '{';
    for (auto itr = s.begin(); itr != s.end();) {
        os << *itr;
        if (++itr != s.end()) os << ',';
    }
    os << '}';
    return os;
}
template <typename T> ostream& operator<<(ostream& os, const unordered_set<T>& s) {
    os << '{';
    for (auto itr = s.begin(); itr != s.end();) {
        os << *itr;
        if (++itr != s.end()) os << ',';
    }
    os << '}';
    return os;
}
template <typename T> ostream& operator<<(ostream& os, const deque<T>& v) {
    for (int i = 0; i < (int)v.size(); i++) {
        os << v[i] << (i + 1 == (int)v.size() ? "" : " ");
    }
    return os;
}

void debug_out() { cerr << '\n'; }
template <class Head, class... Tail> void debug_out(Head&& head, Tail&&... tail) {
    cerr << head;
    if (sizeof...(Tail) > 0) cerr << ", ";
    debug_out(move(tail)...);
}
#ifdef LOCAL
#define debug(...)                                                                   \
    cerr << " ";                                                                     \
    cerr << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]" << '\n'; \
    cerr << " ";                                                                     \
    debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

template <typename T> T gcd(T x, T y) { return y != 0 ? gcd(y, x % y) : x; }
template <typename T> T lcm(T x, T y) { return x / gcd(x, y) * y; }

template <class T1, class T2> inline bool chmin(T1& a, T2 b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T1, class T2> inline bool chmax(T1& a, T2 b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
#pragma endregion

const int INF = 1e9;
const long long IINF = 1e18;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
const char dir[4] = {'D', 'R', 'U', 'L'};
const long long MOD = 1000000007;
// const long long MOD = 998244353;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, S, T, K;
    cin >> N >> S >> T >> K;
    S--, T--;
    vector<int> X(N);
    cin >> X;
    int M;
    cin >> M;
    vector<vector<pair<int, int>>> G(N);
    for (; M--;) {
        int A, B, Y;
        cin >> A >> B >> Y;
        A--, B--;
        G[A].emplace_back(B, Y + X[B]);
    }

    vector<vector<ll>> dp(K + 1, vector<ll>(N, IINF));
    vector<vector<pair<int, int>>> pre(K + 1, vector<pair<int, int>>(N));
    priority_queue<tuple<ll, int, int>> pq;
    auto update = [&](int nx, int ny, int x, int y, ll val) {  // 状態 (x,y) から (nx,ny) に値 val で遷移
        if (chmin(dp[nx][ny], val)) {
            pq.emplace(-dp[nx][ny], nx, ny);
            pre[nx][ny] = make_pair(x, y);
        }
    };
    dp[1][S] = X[S];
    pq.emplace(-dp[1][S], 1, S);

    while (!pq.empty()) {
        auto t = pq.top();
        pq.pop();
        ll val;
        int k, v;
        tie(val, k, v) = t;
        val *= -1;
        if (dp[k][v] < val) continue;
        for (auto& e : G[v]) {
            int u = e.first;
            update(min(K, k + 1), u, k, v, val + e.second);
        }
    }

    ll time = dp[K][T];
    if (time == IINF) {
        cout << "Impossible" << '\n';
        return 0;
    }
    cout << "Possible" << '\n';
    cout << time << '\n';

    vector<int> ans;
    ans.emplace_back(T);
    int x = K, y = T;
    while (!(x == 1 && y == S)) {
        auto p = pre[x][y];
        x = p.first, y = p.second;
        ans.emplace_back(y);
    }
    reverse(ALL(ans));

    cout << ans.size() << '\n';
    for (int i = 0; i < ans.size(); i++) cout << ans[i] + 1 << (i + 1 == ans.size() ? '\n' : ' ');
    return 0;
}