#include<bits/stdc++.h>
using namespace std;
#define int long long
struct no {
	int id;
	int num;
	vector <int > edge;

} a[200005], b[200005];
int vis[200005], ans = -10000000000000000;
bool cmp(no x, no y) {
	return x.num < y.num;
}
void bfs( no i) {
	queue<no> q;
	q.push(i);
	int mj = i.num;
	vis[i.id] = 1;
	while (!q.empty()) {
		no temp = q.front();
		vis[temp.id] = 1;
		q.pop();
		for (int j = 0; j < temp.edge.size(); j++) {
			ans = max(ans, b[temp.edge[j]].num - mj);
			if (!vis[temp.edge[j]])
				q.push(b[temp.edge[j]]);

		}
	}



}



signed main() {
		//freopen("188E.in","r",stdin);
	//	 	freopen("188E.out","w",stdout);
	int n, m, tp, st, ed;
	cin >> n >> m;
	for (int i = 1; i <= n; i++) {
		cin >> tp;
		a[i].id = i;
		a[i].num = tp;
		b[i].id = i;
		b[i].num = tp;
	}
	for (int i = 1; i <= m; i++) {
		cin >> st >> ed;
		a[st].edge.push_back(ed);
		b[st].edge.push_back(ed);
	}

	sort(a + 1, a + n + 1, cmp);
	for (int i = 1; i <= n; i++) {
		if (vis[a[i].id])continue;
		bfs(a[i]);

	}
	cout << ans;

}