#include<iostream>

#include<cstdio>

#include<cstring>

#include<queue>

#define ll long long

using namespace std;

const int N=1e5+,M=5e5+;

int n,m,head1[N],xnt1,head2[N],xnt2;

ll c[N],fn[N],fx[N],mx;

bool vis1[N],vis2[N];

struct Edge{

    int next,to;

    Edge(int n=,int t=):next(n),to(t) {}

}edge1[M<<],edge2[M<<];

void add(int x,int y)

{

    edge1[++xnt1]=Edge(head1[x],y);head1[x]=xnt1;

    edge2[++xnt2]=Edge(head2[y],x);head2[y]=xnt2;

}

void read()

{

    scanf("%d%d",&n,&m);

    for(int i=;i<=n;i++)scanf("%lld",&c[i]);

    int x,y,z;

    for(int i=;i<=m;i++)

    {

        scanf("%d%d%d",&x,&y,&z);

        add(x,y);if(z==)add(y,x);

    }

}

void dj1()

{

    memset(fn,,sizeof fn);

    priority_queue<pair<ll,int> > q;fn[]=c[];q.push(make_pair(fn[],));

    while(q.size())

    {

        int k=q.top().second;q.pop();

        while(vis1[k]&&q.size())k=q.top().second,q.pop();

        if(vis1[k])break;vis1[k]=;

        for(int i=head1[k],v;i;i=edge1[i].next)

            if(min(fn[k],c[v=edge1[i].to])<fn[v])

            {

                fn[v]=min(fn[k],c[v]);q.push(make_pair(fn[v],v));

            }

    }

}

void dj2()

{

    priority_queue<pair<ll,int>,vector<pair<ll,int> >,greater<pair<ll,int> > >q;

    fx[n]=c[n];q.push(make_pair(fx[n],n));

    while(q.size())

    {

        int k=q.top().second;q.pop();

        while(vis2[k]&&q.size())k=q.top().second,q.pop();

        if(vis2[k])break;vis2[k]=;

        for(int i=head2[k],v;i;i=edge2[i].next)

            if(max(fx[k],c[v=edge2[i].to])>fx[v])

            {

                fx[v]=max(fx[k],c[v]);q.push(make_pair(fx[v],v));

            }

    }

}

int main()

{

    read();

    dj1();dj2();

    for(int i=;i<=n;i++)

        if(vis1[i]&&vis2[i])

            mx=max(mx,fx[i]-fn[i]);

    printf("%lld",mx);

    return ;

}