#include<bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;

int main(){
	int n,m;
	cin>>n>>m;
	vector<int>h(n),rev(n);
	rep(i,n){
		cin>>h[i];
		rev[h[i]-1]=i;
	}
	vector<vector<int>>G(n);
	rep(i,m){
		int a,b;
		cin>>a>>b;
		a--;b--;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	vector<int>d1(n,-1e9),d2(n,-1e9);
	d1[0]=0;
	d2[n-1]=0;
	for(auto i:rev){
		for(auto e:G[i]){
			if(h[i]<h[e])d1[e]=max(d1[e],d1[i]+1);
		}
	}
	
	for(auto i:rev){
		for(auto e:G[i]){
			if(h[i]<h[e])d2[e]=max(d2[e],d2[i]+1);
		}
	}
	int ans=-1e9;
	rep(i,n)ans=max(ans,d1[i]+d2[i]);
	if(ans<0)ans=-2;
	cout<<ans+1<<endl;

}