// P1073 最优贸易。价格是 1..100，单调标签至多改善 100 次。
#include <bits/stdc++.h>
using namespace std;
int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    int n, m; if (!(cin >> n >> m)) return 0;
    vector<int> price(n + 1);
    for (int i = 1; i <= n; ++i) cin >> price[i];
    vector<vector<int>> g(n + 1), rg(n + 1);
    auto add = [&](int u, int v) { g[u].push_back(v); rg[v].push_back(u); };
    for (int i = 0, u, v, z; i < m; ++i) {
        cin >> u >> v >> z; add(u,v); if (z == 2) add(v,u);
    }
    vector<int> low(n + 1, 101), high(n + 1, -1);
    vector<bool> inq(n + 1, false);
    queue<int> q; low[1] = price[1]; q.push(1); inq[1] = true;
    while (!q.empty()) {
        int u = q.front(); q.pop(); inq[u] = false;
        for (int v : g[u]) {
            int cand = min(low[u], price[v]);
            if (cand < low[v]) {
                low[v] = cand;
                if (!inq[v]) { q.push(v); inq[v] = true; }
            }
        }
    }
    high[n] = price[n]; q.push(n); inq[n] = true;
    while (!q.empty()) {
        int u = q.front(); q.pop(); inq[u] = false;
        for (int v : rg[u]) {
            int cand = max(high[u], price[v]);
            if (cand > high[v]) {
                high[v] = cand;
                if (!inq[v]) { q.push(v); inq[v] = true; }
            }
        }
    }
    int ans = 0;
    for (int v = 1; v <= n; ++v)
        if (low[v] <= 100 && high[v] >= 1) ans = max(ans, high[v]-low[v]);
    cout << ans << '\n';
}