#include<bits/stdc++.h>
using namespace std;
const int maxn=1e5+100;
struct node {
    int u,v,nxt;
}edge[maxn*10],edge2[maxn*10];
int head[maxn],head2[maxn];
int tot=0,tot2=0;
void addedge (int u,int v) {
    edge[tot].u=u;
    edge[tot].v=v;
    edge[tot].nxt=head[u];
    head[u]=tot++;
}

void addedge2 (int
 
 u,int v) {
    edge2[tot2].u=u;
    edge2[tot2].v=v;
    edge2[tot2].nxt=head2[u];
    head2[u]=tot2++;
} 
int w[maxn],n,m;
int visit[maxn],visit2[maxn];
int d[maxn];//表示從1出發到當前節點所能達到的最小權值
int d2[maxn];//表示從當前節點出發到n所能達到的最大權值
struct qnode {
    int v,w;
    bool operator < (const qnode &r) const {
        
 
return w>r.w;
    }
};
void dijkstra (int s) {
    priority_queue<qnode> q;
    q.push({s,w[s]});
    d[s]=w[s];
    visit[s]=1;
    while (!q.empty()) {
        qnode u=q.top();
        q.pop();
        for (int i=head[u.v];i!=-1;i=edge[i].nxt) {
            int v=edge[i].v;
            d[v]
 
=min(min(w[v],d[v]),d[u.v]);
            if (!visit[v]) q.push({v,d[v]}),visit[v]=1;
            
        }
    }
} 

void dijkstra2 (int s) {
    priority_queue<qnode> q;
    q.push({s,-w[s]});
    d2[s]=w[s];
    visit2[s]=1;
    while (!q.empty()) {
        qnode u=q.top();
        q.pop();
        for (int i=head2[u.v];i!=-1;i=edge2[i].nxt) {
            int v=edge2[i].v;
            d2[v]=max(max(w[v],d2[v]),d2[u.v]);
            if (!visit2[v]) q.push({v,-d2[v]}),visit2[v]=1;
        }
    }
}
int main () {
    scanf("%d%d",&n,&m);
    for (int i=1;i<=n;i++) scanf("%d",&w[i]),head[i]=-1,head2[i]=-1,d[i]=1e9,d2[i]=0;
    for (int i=0;i<m;i++) {
        int x,y,f;
        scanf("%d%d%d",&x,&y,&f);
        addedge(x,y);
        if (f==2)
            addedge(y,x);
        addedge2(y,x);
        if (f==2)
            addedge2(x,y); 
    }
    dijkstra(1);
    dijkstra2(n);
    int Max=0;
    for (int i=1;i<=n;i++) {
        //printf("%d %d %d %d %d\n",i,d[i],d2[i],visit[i],visit2[i]);
        Max=max(Max,d2[i]-d[i]);
    }
    printf("%d\n",Max);
    return 0;
}