#include <iostream>
#include <cstdio>
#include <iomanip>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <utility>
#include <numeric>
#include <algorithm>
#include <functional>
#include <cctype>
#include <complex>
#include <string>
#include <sstream>
#include <fstream>
#include <cassert>
using namespace std;

//common

typedef int  i32;
typedef long long i64,ll;
typedef long double ld;

#define BR "\n"
#define ALL(c) (c).begin(),(c).end()
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define FOR(i,l,r) for(int i=(int)l;i<(int)(r);++i)
#define EACH(it,o) for(auto it = (o).begin(); it != (o).end(); ++it)
#define IN(l,v,r) ((l)<=(v) && (v)<(r))

//config
//#define NDEBUG
//#define INF 1<<30
//#define EPS 1e-8
//const ll MOD =100000007;

//debug
#ifdef NDEBUG
#define DUMP(x)
#define DUMPLN(x)
#define DEBUG(x)
#define DEBUGLN(x)
#define LINE()
#define LINELN()
#define CHECK(exp,act)
#define STOP(e)
#else
#define DUMP(x)  cerr << #x << " = " << (x)
#define DUMPLN(x)  DUMP(x) <<endl
#define DEBUG(x) DUMP(x) << LINE() << " " << __FILE__
#define DEBUGLN(x) DEBUG(x)<<endl
#define LINE()    cerr<< " (L" << __LINE__ << ")"
#define LINELN()    LINE()<<endl
#define CHECK(exp,act)  if(exp!=act){DUMPLN(exp);DEBUGLN(act);}
#define STOP(e)  CHECK(e,true);if(!(e)) exit(1);
#endif

template<class T> inline string toString(const vector<T>& x) {
	stringstream ss;
	REP(i,x.size()){
		if(i!=0)ss<<" ";
		ss<< x[i];
	}
	return ss.str();
}

template<class T> inline string toString(const vector<vector<T> >& map) {
	stringstream ss;
	REP(i,map.size()){
		if(i!=0)ss<<BR;
		ss<< toString(map[i]);
	}
	return ss.str();
}
template<class K,class V>  string toString(map<K,V>& x) {
	string res;stringstream ss;
	for(auto& p:x)ss<< p.first<<":" << p.second<<" ";
	return ss.str();
}

string BITtoString(int bit){
    stringstream ss;
    while(bit!=0){ss<<(bit%2);bit/=2;}
    string res=ss.str();reverse(ALL(res));
    return res;
}

template<typename T> inline T pmod(T v,T MOD){
	return (v%MOD+MOD)%MOD;
}
#define nextInt(n) scanf("%d",&n)
#define defInt(n) int n;nextInt(n)
#define nextLong(n) scanf("%lld",&n)
#define defLong(n) ll n;nextLong(n)
#define nextDouble(n) scanf("%lf",&n)

namespace EGraph{
    typedef double Cost;Cost CINF=1e15;
    struct Edge{
        int from,to;Cost cost;
        Edge(int from,int to,Cost cost)
        : from(from),to(to),cost(cost) {};
        bool operator<(Edge r) const{
            return cost<r.cost;
        }
        bool operator>(Edge r) const{
            return cost>r.cost;
        }
    };
    typedef vector<vector<Edge> >  Graph;

    void  addedge(Graph& g,int a,int b,Cost c){
            g[a].push_back(Edge(a,b,c));
//            g[b].push_back(Edge(b,a,c));
    }
}
using namespace EGraph;

namespace ShortestPath{
    using namespace EGraph;

    struct Task{
        int prev,pos;Cost cost;
        Task(int prev,int pos,Cost cost)
            :prev(prev),pos(pos),cost(cost){};
        bool operator>(const Task& r) const{
            return cost>r.cost;
        }
    };
 
    //verified by codoforces 144D http://codeforces.com/contest/144/submission/4976825
    // // 負の辺がない
    // // O(E*logV)
    vector<Cost> dijkstra(const Graph& g,const int s,vector<int>& prev){
        const int V=g.size();
        vector<Cost> d(V,CINF);d[s]=0;
        fill(ALL(prev), -2);
        priority_queue<Task,vector<Task>,greater<Task> > que;
        que.push(Task(-1,s,0));
        while(!que.empty()){
            Task task=que.top();que.pop();
            //if(prev[task.pos]!=-2)continue;
            if(d[task.pos]<task.cost)continue;
            prev[task.pos]=task.prev;
            EACH(e,g[task.pos]){
                if(d[e->to]>d[e->from]+e->cost){
                    d[e->to]=d[e->from]+e->cost;
                    que.push(Task(e->from,e->to,d[e->to]));
                }
            }   
        }
        return d;
    }
    vector<Cost> dijkstra(const Graph& g,const int s){
        vector<int> prev(g.size());return dijkstra(g,s,prev);
    }

}

using namespace ShortestPath;

class Main{
public:

        int N,M,P,A,B;

        vector<int> ts;
        Graph g;

        int enc(int x,int bit){
            return x*(1<<N)+bit;
        }

        bool input(){
            //   ifstream cin("in");
            //  ofstream cout( "out" );
            nextInt(N);nextInt(M);nextInt(P);nextInt(A);nextInt(B);A--;B--; if(N==0)return false;
            ts=vector<int> (N);REP(i,N) nextInt(ts[i]);//馬車券と頭数
            g=Graph(M*(1<<N));
            REP(i,P){
                int x,y;double z;nextInt(x);nextInt(y);nextDouble(z);x--;y--;
                REP(bit,1<<N){
                    REP(c,N)if((bit>>c)&1){
                        addedge(g,enc(x,bit),enc(y,bit-(1<<c)),z/ts[c]);
                        addedge(g,enc(y,bit),enc(x,bit-(1<<c)),z/ts[c]);
                    }
                }
            }
            return true;
        }

        void run(){
            while(input()){
                //30*2^8
                Cost mv=CINF;
                vector<double> res=dijkstra(g,enc(A,(1<<N) -1));
                REP(bit,1<<N)mv=min(mv,res[enc(B,bit)]);

                if(mv!=CINF) cout << mv<<endl;
                else  cout << "Impossible"<<endl;
            }
        }
};

int main(){
    cout <<fixed<<setprecision(15);	
    ios::sync_with_stdio(false);
    Main().run();
    return 0;
}

Measured memory_bytes: 24048