#include <cstdio>

 #include <cstring>

 #include <vector>

 using namespace std;

 const int N = ;

 int f[N], x, y;

 double mid;

 struct Edge{

     int p, t;

     double w;

     inline void change() {

         w = mid * (double)t - f[p];

     }

 };

 vector < Edge > G[N];

 bool vis[N];

 double dis[N];

 bool spfa(const int &z){

     vis[z] = true;

     for(int i = ; i < G[z].size(); i++)

         if (dis[G[z][i].p] > dis[z] + G[z][i].w) {

             if (vis[G[z][i].p])

                 return true;

             else {

                 dis[G[z][i].p] = dis[z] + G[z][i].w;

                 if (spfa(G[z][i].p))

                     return true;

             }

         }

     vis[z] = false;

     return false;

 }

 inline bool judge(){

     for (int i = ; i <= x; i++)

         for (int j = ; j < G[i].size(); j++)

             G[i][j].change();

     memset(vis, , sizeof(vis));

     memset(dis, , sizeof(dis));

     for (int i = ; i <= x; i++)

         if (spfa(i))

             return true;

     return false;

 }

 int main() {

     scanf("%d %d", &x, &y);

     for (int i = ; i <= x; i++)

         scanf("%d", &f[i]);

     for (int i = ; i <= y; i++) {

         int m, n, o;

         scanf("%d %d %d", &m, &n, &o);

         G[m].push_back((Edge) {n, o, });

     }

     double l = , r = ;

     while (r - l > 0.000001) {

         mid = (l + r) / ;

         if (judge())    l = mid;

         else    r = mid;

     }

     printf("%.2lf", l);

     return ;

 }