#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
#include<vector>
struct UF{
	int n;
	vector<int>parent,rank,mx;
	UF(int n_=0):n(n_),parent(n_),rank(n_,1),mx(n_,(int)-1e9)
	{
		for(int i=0;i<n_;i++)parent[i]=i;
	}
	int find(int a){return parent[a]!=a?parent[a]=find(parent[a]):a;}
	bool same(int a,int b){return find(a)==find(b);}
	bool unite(int a,int b)
	{
		a=find(a),b=find(b);
		if(a==b)return false;
		if(rank[a]<rank[b])
		{
			mx[b]=max(mx[b],mx[a]);
			parent[a]=b;
			rank[b]+=rank[a];
		}
		else
		{
			mx[a]=max(mx[a],mx[b]);
			parent[b]=a;
			rank[a]+=rank[b];
		}
		return true;
	}
	int size(int a){return rank[find(a)];}
};
int N,M,S,T;
int P[1<<17];
vector<int>G[1<<17];
int dp[1<<17];
int id[1<<17];
main()
{
	cin>>N>>M>>S>>T;
	S--,T--;
	for(int i=0;i<N;i++)cin>>P[i];
	for(int i=0;i<M;i++)
	{
		int a,b;cin>>a>>b;
		a--,b--;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	for(int i=0;i<N;i++)id[i]=i;
	sort(id,id+N,[](int i,int j){return P[i]>P[j];});
	UF uf(N);
	for(int idx=0;idx<N;idx++)
	{
		int u=id[idx];
		for(int v:G[u])if(P[v]>P[u])uf.unite(u,v);
		int mx=uf.mx[uf.find(u)];
		mx++;
		if(u==S)mx=0;
		uf.mx[uf.find(u)]=mx;
		if(idx+1<N&&P[id[idx]]>P[id[idx+1]])
		{
			for(int i=idx;i>=0&&P[id[idx]]==P[id[i]];i--)
			{
				for(int v:G[id[i]])if(P[v]==P[id[i]])uf.unite(v,id[i]);
			}
		}
	}
	cout<<uf.mx[uf.find(T)]<<endl;
}