import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] first = br.readLine().split(" ", 4);
        int n = Integer.parseInt(first[0]);
        int m = Integer.parseInt(first[1]);
        int s = Integer.parseInt(first[2]) - 1;
        int t = Integer.parseInt(first[3]) - 1;
        String[] second = br.readLine().split(" ", n);
        Town[] towns = new Town[n];
        ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            towns[i] = new Town(i, Integer.parseInt(second[i]));
            graph.add(new ArrayList<>());
        }
        for (int i = 0; i < m; i++) {
            String[] line = br.readLine().split(" ", 2);
            int a = Integer.parseInt(line[0]) - 1;
            int b = Integer.parseInt(line[1]) - 1;
            graph.get(a).add(b);
            graph.get(b).add(a);
        }
        PriorityQueue<Town> queue = new PriorityQueue<>();
        queue.add(towns[s]);
        boolean[] visited = new boolean[n];
        visited[s] = true;
        int score = Integer.MAX_VALUE;
        int count = 0;
        while (queue.size() > 0) {
            Town y = queue.poll();
            if (score > y.value) {
                score = y.value;
                count++;
            }
            for (int x : graph.get(y.idx)) {
                if (!visited[x]) {
                    queue.add(towns[x]);
                    visited[x] = true;
                }
            }
        }
        System.out.println(count - 1);
    }
    
    static class Town implements Comparable<Town> {
        int idx;
        int value;
        
        public Town(int idx, int value) {
            this.idx = idx;
            this.value = value;
        }
        
        public int compareTo(Town another) {
            return another.value - value;
        }
    }
}