import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int n = Integer.parseInt(sa[0]);
		int m = Integer.parseInt(sa[1]);
		int s = Integer.parseInt(sa[2]) - 1;
		int t = Integer.parseInt(sa[3]) - 1;
		sa = br.readLine().split(" ");
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = Integer.parseInt(sa[i]);
		}
		List<List<Integer>> list = new ArrayList<>(n);
		for (int i = 0; i < n; i++) {
			list.add(new ArrayList<>());
		}
		for (int i = 0; i < m; i++) {
			sa = br.readLine().split(" ");
			int a = Integer.parseInt(sa[0]) - 1;
			int b = Integer.parseInt(sa[1]) - 1;
			list.get(a).add(b);
			list.get(b).add(a);
		}
		br.close();

		int[] d = new int[list.size()];
		PriorityQueue<Node> que = new PriorityQueue<Node>();
		Node first = new Node(s, 0, p[s]);
		que.add(first);

		while (!que.isEmpty()) {
			Node cur = que.poll();
			if (cur.d < d[cur.v]) {
				continue;
			}
			for (int next : list.get(cur.v)) {
				int alt = d[cur.v];
				if (cur.x > p[next]) {
					alt++;
				}
				if (alt > d[next]) {
					d[next] = alt;
					que.add(new Node(next, alt, Math.min(cur.x, p[next])));
				}
			}
		}
		System.out.println(d[t]);
	}

	static class Node implements Comparable<Node> {
		int v, d, x;

		public Node(int v, int d, int x) {
			this.v = v;
			this.d = d;
			this.x = x;
		}

		public int compareTo(Node o) {
			if (d != o.d) {
				return o.d - d;
			}
			return o.x - x;
		}
	}
}