#include <cstdio>
#include <cstring>
inline int max(int a,int b)
{
    return a>b?a:b;
}
inline int min(int a,int b)
{
    return a<b?a:b;
}
typedef struct Edge
{
    int to;
    Edge* next;
    Edge(int t,Edge* n):to(t),next(n) {}
}*lpEdge;
const int MAXN=100001;
lpEdge G1[MAXN],G2[MAXN];
#define addEdge1(x,y) G1[(x)]=new Edge((y),G1[(x)])
#define addEdge2(x,y) G2[(x)]=new Edge((y),G2[(x)])
int n,m;
int price[MAXN],mmax[MAXN],mmin[MAXN],que[MAXN<<2];
void getmin()
{
    int head,tail,x;
    head=tail=0;
    que[tail++]=1;
    mmin[1]=price[1];
    while(head<tail)
        for(lpEdge cur=G1[x=que[head++]]; cur; cur=cur->next)
            if(mmin[cur->to]>min(mmin[x],price[cur->to]))
                mmin[cur->to]=min(mmin[x],price[cur->to]),que[tail++]=cur->to;
}
void getmax()
{
    int head,tail,x;
    head=tail=0;
    que[tail++]=n;
    mmax[n]=price[n];
    while(head<tail)
        for(lpEdge cur=G2[x=que[head++]]; cur; cur=cur->next)
            if(mmax[cur->to]<max(mmax[x],price[cur->to]))
                mmax[cur->to]=max(mmax[x],price[cur->to]),que[tail++]=cur->to;
}
int main()
{
    scanf("%d%d",&n,&m);
    for(int i=1; i<=n; i++) scanf("%d",price+i);
    for(int i=0,x,y,z; i<m; i++)
    {
        scanf("%d%d%d",&x,&y,&z);
        addEdge1(x,y),addEdge2(y,x);
        if(z==2) addEdge1(y,x),addEdge2(x,y);
    }
    memset(mmax,0,sizeof(mmax));
    memset(mmin,0x3f3f3f3f,sizeof(mmin));
    getmax();
    getmin();
    int ans=0;
    for(int i=1; i<=n; i++)
        ans=max(ans,mmax[i]-mmin[i]);
    printf("%d",ans);
    return 0;
}