#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<set>
#include<map>
#include<vector>
#include<queue>
#include<stack>
using namespace std;
#define ll long long
#define RG register
#define MAX 1111
inline int read()
{
    RG int x=0,t=1;RG char ch=getchar();
    while((ch<'0'||ch>'9')&&ch!='-')ch=getchar();
    if(ch=='-')t=-1,ch=getchar();
    while(ch<='9'&&ch>='0')x=x*10+ch-48,ch=getchar();
    return x*t;
}
int n,m,U[5555],V[5555],W[5555];
int a[MAX];
struct Line{int v,next;double w;}e[5555];
int h[MAX],cnt=1;
inline void Add(int u,int v,double w){e[cnt]=(Line){v,h[u],w};h[u]=cnt++;}
stack<int> S;
int ins[MAX];
double dis[MAX];
bool vis[MAX];
bool SPFA()
{
    while(!S.empty())S.pop();
    for(int i=1;i<=n;++i)vis[i]=true,ins[i]=1,S.push(i),dis[i]=0;
    while(!S.empty())
    {
        int u=S.top();S.pop();
        for(int i=h[u];i;i=e[i].next)
        {
            int v=e[i].v;
            if(dis[v]>dis[u]+e[i].w)
            {
                dis[v]=dis[u]+e[i].w;
                if(!vis[v])S.push(v),vis[v]=true,++ins[v];
                if(ins[v]>=n)return true;
            }
        }
        vis[u]=false;
    }
    return false;
}
bool check(double mid)
{
    for(int i=1;i<=n;++i)h[i]=0;cnt=1;
    for(int i=1;i<=m;++i)Add(U[i],V[i],1.0*W[i]*mid-a[V[i]]);
    if(SPFA())return true;
    return false;
}
int main()
{
    n=read();m=read();
    for(int i=1;i<=n;++i)a[i]=read();
    for(int i=1;i<=m;++i)U[i]=read(),V[i]=read(),W[i]=read();
    double l=0,r=1e6;
    while(r-l>1e-3)
    {
        double mid=(l+r)/2;
        if(check(mid))l=mid;
        else r=mid;
    }
    printf("%.2f\n",l);
    return 0;
}