import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int s = sc.nextInt() - 1;
        int t = sc.nextInt() - 1;
        Town[] towns = new Town[n];
        ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            towns[i] = new Town(i, sc.nextInt());
            graph.add(new ArrayList<>());
        }
        for (int i = 0; i < m; i++) {
            int a = sc.nextInt() - 1;
            int b = sc.nextInt() - 1;
            graph.get(a).add(b);
            graph.get(b).add(a);
        }
        PriorityQueue<Town> queue = new PriorityQueue<>();
        queue.add(towns[s]);
        HashSet<Integer> visited = new HashSet<>();
        int score = Integer.MAX_VALUE;
        int count = 0;
        while (queue.size() > 0) {
            Town y = queue.poll();
            if (score > y.value) {
                score = y.value;
                count++;
            }
            visited.add(y.idx);
            for (int x : graph.get(y.idx)) {
                if (!visited.contains(x)) {
                    queue.add(towns[x]);
                }
            }
        }
        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;
        }
    }
}