#include <bits/stdc++.h>
using namespace std;


#include <algorithm>
#include <cassert>
#include <vector>

namespace atcoder {

struct dsu {
  public:
    dsu() : _n(0) {}
    explicit dsu(int n) : _n(n), parent_or_size(n, -1) {}

    int merge(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        int x = leader(a), y = leader(b);
        if (x == y) return x;
        if (-parent_or_size[x] < -parent_or_size[y]) std::swap(x, y);
        parent_or_size[x] += parent_or_size[y];
        parent_or_size[y] = x;
        return x;
    }

    bool same(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        return leader(a) == leader(b);
    }

    int leader(int a) {
        assert(0 <= a && a < _n);
        if (parent_or_size[a] < 0) return a;
        return parent_or_size[a] = leader(parent_or_size[a]);
    }

    int size(int a) {
        assert(0 <= a && a < _n);
        return -parent_or_size[leader(a)];
    }

    std::vector<std::vector<int>> groups() {
        std::vector<int> leader_buf(_n), group_size(_n);
        for (int i = 0; i < _n; i++) {
            leader_buf[i] = leader(i);
            group_size[leader_buf[i]]++;
        }
        std::vector<std::vector<int>> result(_n);
        for (int i = 0; i < _n; i++) {
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < _n; i++) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
            std::remove_if(result.begin(), result.end(),
                           [&](const std::vector<int>& v) { return v.empty(); }),
            result.end());
        return result;
    }

  private:
    int _n;
    std::vector<int> parent_or_size;
};

}  // namespace atcoder

using namespace atcoder;

using ll = long long;
using ld = long double;
#define fi first
#define se second
#define pb push_back

int main(){
  int n,m,s,t;
  cin>>n>>m>>s>>t;
  s--;
  t--;
  
  int p[n];
  int copy[n];
  int newnumber[n];
  int oldnumber[n];
  int newp[n];
  
  for(int i=0;i<n;i++){
    cin>>p[i];
    copy[i]=p[i];
  }
  
  sort(copy,copy+n);
  reverse(copy,copy+n);
  
  map<int,int> rank;
  //rank[順位]=人数
  map<int,int> seen;
  
  for(int i=0;i<n;i++){
    rank[copy[i]]=i;
  }
  
  for(int i=0;i<n;i++){
    newnumber[i]=rank[p[i]]-seen[p[i]];
    oldnumber[newnumber[i]]=i;
    newp[newnumber[i]]=p[i];
    seen[p[i]]++;
  }
  
  /*for(int i=0;i<n;i++){
    cout<<newnumber[i]<<" ";
  }
  cout<<endl;*/
  
  s=newnumber[s],t=newnumber[t];
  
  
  vector<vector<int>> graph(n);
  for(int i=0;i<m;i++){
    int a,b;
    cin>>a>>b;
    a--;
    b--;
    a=newnumber[a],b=newnumber[b];
    graph[a].pb(b);
    graph[b].pb(a);
  }
  
  int dp[n];
  int dp2[n];
  dsu d(n);
  
  for(int i=0;i<n;i++){
    dp[i]=-1*1e9;
    dp2[i]=newp[i];
  }
  
  int now=-1*1e9;
  
  for(int i=0;i<n;i++){
    if(i==s){
      dp[i]=0;
    }
    if(graph[i].size()!=0){
      for(int next:graph[i]){
        if(next<i){
          int p=d.leader(next),q=d.leader(i);
          if(dp2[p]>newp[i]){
            dp[i]=max(dp[i],dp[p]+1);
          }
          else{
            dp[i]=max(dp[i],dp[p]);
          }
          d.merge(next,i);
          int r=d.leader(i);
          dp[r]=max(dp[r],dp[i]);
          dp2[r]=min({dp2[r],dp2[q],dp2[p],newp[i],newp[next]});
        }
      }
    }
  }
  
  int ans=0;
  for(int i=0;i<n;i++){
    ans=max(ans,dp[i]);
  }  
  cout<<ans<<endl;
}