/* -*- coding: utf-8 -*-
 *
 * 1382.cc:  No.1382 Travel in Mitaru city - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

typedef pair<int,int> pii;
typedef vector<int> vi;

/* global variables */

int ps[MAX_N];
vi nbrs[MAX_N];
bool used[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, m, st, gl;
  scanf("%d%d%d%d", &n, &m, &st, &gl);
  st--, gl--;

  for (int i = 0; i < n; i++) scanf("%d", ps + i);

  for (int i = 0; i < m; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    a--, b--;
    nbrs[a].push_back(b);
    nbrs[b].push_back(a);
  }

  int x = ps[st], y = 0;
  used[st] = true;

  priority_queue<pii> q;
  q.push(pii(ps[st], st));

  while (! q.empty()) {
    pii u = q.top(); q.pop();
    int up = u.first, ui = u.second;
    //printf("u=(%d,%d), x=%d, y=%d\n", up, ui, x, y);

    if (x > up) x = up, y++;
    
    vi &nbru = nbrs[ui];
    for (vi::iterator vit = nbru.begin(); vit != nbru.end(); vit++) {
      int v = *vit;
      if (! used[v]) {
	used[v] = true;
	q.push(pii(ps[v], v));
      }
    }
  }

  printf("%d\n", y);
  return 0;
}