#include"bits/stdc++.h"
using namespace std;int n,m,i,k=-1,c,h[1<<17],u[1<<17],d[1<<17],p[1<<17];vector<int>g[1<<17];
int main(){for(cin>>n>>m;i<n;cin>>h[p[i]=i],i++);sort(p,p+n,[](int i,int j){return h[i]<h[j];});while(m--)cin>>i>>c,g[--i].push_back(--c),g[c].push_back(i);u[0]=d[n-1]=1;for(i=0;i<n;i++){m=p[i];for(int t:g[m])if(h[t]>h[m]){if(u[m])u[t]=max(u[t],u[m]+1);if(d[m])d[t]=max(d[t],d[m]+1);}}for(i=0;i<n;i++)if(u[i]&&d[i]&&u[i]+d[i]-1>k)k=u[i]+d[i]-1;cout<<k<<endl;}