#if __has_include("../library/Basic/Debug.hpp")

#include "../library/Basic/Debug.hpp"

#else

/* ----- Header Files ----- */
// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <string>
#include <tuple>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>
#include <cstdint>


/* ----- Type Alias ----- */
using Bool = bool;
using Int = long long int;
using Real = long double;
using Char = char;
using String = std::string;
template <class... Ts>
using Tuple = std::tuple<Ts...>;

template <class T>
using Vector = std::vector<T>;
template <class T>
using Matrix = Vector<Vector<T>>;
template <class T>
using Queue = std::queue<T>;
template <class T>
using Stack = std::stack<T>;
template <class T>
using Deque = std::deque<T>;

template <class T>
using MaxHeap = std::priority_queue<T>;
template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;
template <class T>
using Set = std::set<T>;
template <class T, class U>
using Map = std::map<T, U>;

template <class T, class... Us>
using Func = std::function<T(Us...)>;

template <class T>
T genv(T v) { return v; }

template <class T, class... Ts>
auto genv(size_t l, Ts... ts) {
    return Vector<decltype(genv<T>(ts...))>(l, genv<T>(ts...));
}

template <class Cost = Int>
struct Edge {
    Int src, dst;
    Cost cost;
    Edge(Int src = -1, Int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = Int>
using Edges = Vector<Edge<Cost>>;
template <class Cost = Int>
using Graph = Vector<Vector<Edge<Cost>>>;

#endif

/* ----- Misc ----- */
void fastio() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

struct Fout {
    Int precision;
    Fout(Int precision) : precision(precision) {}
};
std::ostream& operator<<(std::ostream& os, const Fout& fio) {
    os << std::fixed << std::setprecision(fio.precision);
    return os;
}


/* ----- Constants ----- */
// constexpr Int INF = std::numeric_limits<Int>::max() / 3;
constexpr Real INF = std::numeric_limits<Real>::max() / 10;
// constexpr Int MOD = 1000000007;
// constexpr Real PI = acos(-1);
// constexpr Real EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));

Bool solve() {
    Int p, n, m, s, g;
    std::cin >> p >> n >> m >> s >> g;
    if (p == 0) return false;
    --s, --g;

    Vector<Real> t(p);
    for (auto& x : t) std::cin >> x;

    Graph<Real> graph(n);
    for (Int i = 0; i < m; ++i) {
        Int u, v;
        Real d;
        std::cin >> u >> v >> d;
        --u, --v;
        graph[u].emplace_back(u, v, d);
        graph[v].emplace_back(v, u, d);
    }

    auto dp = genv<Real>(n, 1 << p, INF);
    dp[s][0] = 0;

    MinHeap<Tuple<Real, Int, Int>> heap;
    heap.emplace(0, s, 0);

    while (!heap.empty()) {
        Real d;
        Int v, b;
        std::tie(d, v, b) = heap.top();
        heap.pop();
        if (d > dp[v][b]) continue;

        for (auto e : graph[v]) {
            for (Int i = 0; i < p; ++i) {
                if ((b >> i) & 1) continue;
                Int nb = (b | (1 << i));

                Real dx = e.cost / t[i];
                if (dp[e.dst][nb] > dp[v][b] + dx) {
                    dp[e.dst][nb] = dp[v][b] + dx;
                    heap.emplace(dp[e.dst][nb], e.dst, nb);
                }
            }
        }
    }

    Real ans = *std::min_element(dp[g].begin(), dp[g].end());
    if (ans == INF) {
        std::cout << "Impossible" << std::endl;
    } else {
        std::cout << Fout(3) << ans << std::endl;
    }
    return true;
}

int main() {
    while (solve()) {}
    return 0;
}



Measured memory_bytes: 6204