#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++]);
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(int v:p)for(int t:g[v])if(h[t]>h[v]){
if(u[v])u[t]=max(u[t],u[v]+1);
if(d[v])d[t]=max(d[t],d[v]+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;
}