#include<bits/stdc++.h>
using namespace std;
const int MAX_N = 1e5+2;
int n,m,s,t;
int u0,v0;
vector<int> adj[MAX_N];
int p[MAX_N];
bool used[MAX_N];
priority_queue< pair<int,int> > pq;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    cin>>n>>m>>s>>t;
    for(int i=1; i<=n; i++)
    {
        cin>>p[i];
    }
    for(int i=0; i<m; i++)
    {
        cin>>u0>>v0;
        adj[u0].push_back(v0);
        adj[v0].push_back(u0);
    }
    int ans = 0;
    int val = p[s];
    used[s] = true;
    pq.push({p[s],s});
    ///cout<<endl;
    while(!pq.empty())
    {
        pair<int,int> tmp = pq.top();
        ///cout<<tmp.first<<" "<<tmp.second<<endl;
        pq.pop();
        if(val > tmp.first)
        {
            val = tmp.first;
            ans++;
        }
        for(auto x: adj[tmp.second])
        {
            if(used[x] == 0)
            {
                used[x] = 1;
                pq.push({p[x],x});
            }
        }
    }
    if(used[t])cout<<ans<<endl;
    else cout<<0<<endl;
}