//01分数问题 + SPFA问题
#include <bits/stdc++.h>
using namespace std;
const int N = 1010, M = 5010;
int h[N], e[M], ne[M], w[M], idx;
int f[N];
double  dist[N];
int  cnt[N];
bool st[N];
int l, p;

void add(int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++;
}
//求正环
bool check(double mid)
{
    queue<int> q;
    memset(st, 0, sizeof st);
    memset(dist, 0, sizeof dist);
    memset(cnt, 0, sizeof cnt);

    for (int i = 1; i <= l; i ++)
    {
        q.push(i);
        st[i] = true;
    }

    while (q.size())
    {
        int t = q.front();
        q.pop();
        st[t] = false;
        for (int i = h[t]; ~i; i = ne[i])
        {
            int j = e[i];
            //求负环
            //if (dist[j] > dist[t]  + mid * w[i] - f[j])
            if (dist[j] < dist[t] + f[j] - mid * w[i])
            {
                //求负环
                //dist[j] = dist[t]  + mid * w[i] - f[j];
                dist[j] = dist[t] + f[j] - mid * w[i];
                cnt[j] = cnt[t] + 1;
                if (cnt[j] >= l) return true;
                if (!st[j])
                {
                    q.push(j);
                    st[j] = true;
                }
            }
        }
    }
    return false;
}

int main(void)
{
    memset(h, -1, sizeof h);
    cin >> l >> p;
    for (int i = 1; i <= l; i ++)
        cin >> f[i];
    for (int i = 0; i < p; i ++)
    {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
    }

    double l = 0, r = 1000;
    while (r - l > 1e-4)
    {
        double mid = (r + l) / 2;
        if (check(mid)) l = mid;
        else r = mid;
    }
    printf("%.2lf\n", l);
    return 0;
}