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//#pragma comment(linker, "/STACK:1024000000,1024000000") #include<cstdio> #include<cstring> #include<cstdlib> #include<algorithm> #include<iostream> #include<sstream> #include<cmath> #include<climits> #include<string> #include<map> #include<queue> #include<vector> #include<stack> #include<set> using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair<int,int> pii; #define pb(a) push(a) #define INF 0x1f1f1f1f #define lson idx<<1,l,mid #define rson idx<<1|1,mid+1,r #define PI 3.1415926535898 template<class T> T min(const T& a,const T& b,const T& c) { return min(min(a,b),min(a,c)); } template<class T> T max(const T& a,const T& b,const T& c) { return max(max(a,b),max(a,c)); } void debug() { #ifdef ONLINE_JUDGE #else freopen("d:\in1.txt","r",stdin); freopen("d:\out1.txt","w",stdout); #endif } int getch() { int ch; while((ch=getchar())!=EOF) { if(ch!=' '&&ch!=' ')return ch; } return EOF; } double dp[33][1<<8]; int t[8]; int g[33][33]; int n,m,p,a,b; int read() { scanf("%d%d%d%d%d",&n,&m,&p,&a,&b); if(n==0)return 0; for(int i=0;i<n;i++) scanf("%d",&t[i]); memset(g,-1,sizeof(g)); for(int i=1;i<=p;i++) { int u,v,w; scanf("%d%d%d",&u,&v,&w); g[u][v]=g[v][u]=w; } return 1; } double dfs(int u,int k,int st) { if(u==b)return 0; if(dp[u][st]>=0)return dp[u][st]; if(k==n)return INF; double &ans=dp[u][st]; ans=INF; for(int i=1;i<=m;i++)if(g[u][i]!=-1) { for(int j=0;j<n;j++)if(!(st&(1<<j))) { ans=min(ans,(double)g[u][i]/t[j]+dfs(i,k+1,st|(1<<j))); } } return ans; } int main() { while(read()) { memset(dp,-1,sizeof(dp)); double res=dfs(a,0,0); if(res>=INF)printf("Impossible "); else printf("%lf ",res); } return 0; }