#include <stdio.h>
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

int N,M,S,T;
vector<int> p;
vector<vector<int>> E;
int main(){
	
	cin>>N>>M>>S>>T;
	
	S--;T--;
	
	p.resize(N);
	rep(i,N){
		cin>>p[i];
	}
	
	E.resize(N);
	
	rep(i,M){
		int a,b;
		scanf("%d %d",&a,&b);
		a--;b--;
		
		E[a].push_back(b);
		E[b].push_back(a);
	}
	
	priority_queue<pair<int,int>> Q;
	Q.emplace(p[S],S);
	
	int last = Inf;
	int ans = 0;
	
	vector<bool> visited(N,false);
	visited[S] = true;
	
	while(Q.size()>0){
		int u = Q.top().first;
		int v = Q.top().second;
		Q.pop();
		
		if(u < last){
			 last=  u;
			 ans++;
		}
		rep(i,E[v].size()){
			int x = E[v][i];
			if(visited[x])continue;
			visited[x] = true;
			Q.emplace(p[x],x);
		}
		
		
	}
	
	cout<<ans-1<<endl;
	
	return 0;
}