#include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<cstring>
using namespace std;
const int N = 1e5 + 5, M = 5e5 + 5;
int head1[N], head2[N], ver1[M], ver2[M], Next1[M], Next2[M], w[N], d1[N], d2[N];
int n, m, tot1, tot2, ans;
void spfamin(int* head, int* ver, int* Next,int start)
{
	queue<int>q;
	bool v[N];
	memset(v, 0, sizeof(v));
	memset(d1, 0x3f, sizeof(d1));
	d1[start] = w[start], v[start] = 1;
	q.push(start);
	while (q.size())
	{
		int x = q.front(); q.pop();
		v[x] = 0;
		for (int i = head[x]; i; i = Next[i])
		{
			int y = ver[i];
			if (d1[y] > min(d1[x], w[y]))
			{
				d1[y] = min(d1[x], w[y]);
				if (!v[y])	q.push(y), v[y] = 1;
			}
		}
	}
}  

void spfamax(int* head, int* ver, int* Next, int start)
{
	queue<int>q;
	bool v[N];
	memset(v, 0, sizeof(v));
	d2[start] = w[start], v[start] = 1;
	q.push(start);
	while (q.size())
	{
		int x = q.front(); q.pop();
		v[x] = 0;
		for (int i = head[x]; i; i = Next[i])
		{
			int y = ver[i];
			if (d2[y] < max(d2[x], w[y]))
			{
				d2[y] = max(d2[x], w[y]);
				if (!v[y])	q.push(y), v[y] = 1;
			}
		}

	}
}

int main()
{
	ios::sync_with_stdio(0);
	cin >> n >> m;
	for (int i = 1; i <= n; i++)	
	{
		cin >> w[i];
	}
	for (int i = 1; i <= m; i++)
	{
		int x, y, z;
		cin >> x >> y >> z;
		if (z == 1)
		{
			ver1[++tot1] = y, Next1[tot1] = head1[x], head1[x] = tot1;
			ver2[++tot2] = x, Next2[tot2] = head1[y], head2[y] = tot2;
		}
		else
		{
			ver1[++tot1] = y, Next1[tot1] = head1[x], head1[x] = tot1;
			ver2[++tot2] = x, Next2[tot2] = head1[y], head2[y] = tot2;
			ver1[++tot1] = x, Next1[tot1] = head1[y], head1[y] = tot1;
			ver2[++tot2] = y, Next2[tot2] = head1[x], head2[x] = tot2;
		}
	}
	spfamin(head1, ver1, Next1, 1);
	spfamax(head2, ver2, Next2, n);
	for (int i = 1; i <= n; i++)
	{
		ans = max(ans, d2[i] - d1[i]);
	}
	if (ans == 0)	cout << 0;
	else
	cout << ans;
	return 0;
}