#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#define maxv 1050

#define maxe 10050

#define inf 2000000000

#define eps 1e-3

using namespace std;

int n,m,val[maxv],nume=,g[maxv],x,y,z,flag=;

struct edge

{

    int v,c,nxt;

    double w;

}e[maxe];

double dis[maxv];

bool vis[maxv];

void addedge(int u,int v,int c)

{

    e[++nume].v=v;e[nume].c=c;

    e[nume].nxt=g[u];g[u]=nume;

}

void rebuild(double x)

{

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

        e[i].w=e[i].c*x-val[e[i].v];

}

void spfa(int x)

{

    vis[x]=true;

    for (int i=g[x];i;i=e[i].nxt)

    {

        int v=e[i].v;

        if (dis[v]>dis[x]+e[i].w)

        {

            if (vis[v]) {flag=;break;}

            else {dis[v]=dis[x]+e[i].w;spfa(v);}

        }

    }

    vis[x]=false;

}

bool check(double x)

{

    rebuild(x);

    for (int i=;i<=n;i++) dis[i]=inf;

    dis[]=-val[];flag=;spfa();

    return flag;

}

void binary_search()

{

    double l=,r=inf,ans;

    while (r-l>=eps)

    {

        double mid=(l+r)/;

        if (check(mid)) {ans=mid;l=mid;}

        else r=mid;

    }

    printf("%.2lf\n",ans);

}

int main()

{

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

    for (int i=;i<=n;i++) scanf("%d",&val[i]);

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

    {

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

        addedge(x,y,z);

    }

    binary_search();

    return ;

}