#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// int t;cin>>t;
// while(t--){
int n,m;cin>>n>>m;
vector<int> v(n+1);
for (int i = 1; i < n+1; i++)
{
cin>>v[i];
}
double ans=0;
for (int i = 0; i < m; i++)
{
int a,b,c;
cin>>a>>b>>c;
ans=max(ans,double(v[a]+v[b])/c);
}
cout<<fixed<<setprecision(9)<<ans;
// }
return 0;
}
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