#include<bits/stdc++.h>
using namespace std;
const int MAX_N = 1e5+2;
int n,m,s,t;
int u0,v0;
int p[MAX_N];
int dist[MAX_N];
vector<int> adj[MAX_N];
void bfs()
{
    priority_queue< pair<int, pair<int,int> > > pq; /// y , x , v
    pq.push({0,{p[s],s}});
    while(!pq.empty())
    {
        pair<int, pair<int,int> > tmp = pq.top();
        pq.pop();
        if(dist[tmp.second.second] > tmp.first) continue;
        dist[tmp.second.second] = tmp.first;
        if(tmp.second.second == t) continue;
        for(auto x : adj[tmp.second.second])
        {
            if(p[x] < tmp.second.first && dist[x] < dist[tmp.second.second]+1)
            {
                pq.push({tmp.first+1,{p[x],x}});
            }
            else if(p[x] >= tmp.second.first && dist[x] < dist[tmp.second.second])
            {
                pq.push({tmp.first,{tmp.second.first,x}});
            }
        }
    }
    cout<<dist[t]<<endl;
}
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);
    }
    bfs();
}