#include <stdio.h>

typedef struct {
	int key, id;
} data;

typedef struct {
	data obj[100001];
	int size;
} max_heap;

void push(data x, max_heap* h)
{
	int i = ++(h->size), j = i >> 1;
	data tmp;
	h->obj[i] = x;
	while (j > 0) {
		if (h->obj[i].key > h->obj[j].key) {
			tmp = h->obj[j];
			h->obj[j] = h->obj[i];
			h->obj[i] = tmp;
			i = j;
			j >>= 1;
		} else break;
	}
}

data pop(max_heap* h)
{
	int i = 1, j = 2;
	data output = h->obj[1], tmp;
	h->obj[1] = h->obj[(h->size)--];
	while (j <= h->size) {
		if (j < h->size && h->obj[j^1].key > h->obj[j].key) j ^= 1;
		if (h->obj[j].key > h->obj[i].key) {
			tmp = h->obj[j];
			h->obj[j] = h->obj[i];
			h->obj[i] = tmp;
			i = j;
			j <<= 1;
		} else break;
	}
	return output;
}

typedef struct List {
	struct List *next;
	int v;
} list;

int main()
{
	int i, N, M, S, T, u, w, P[100001];
	list *adj[100001] = {}, e[200001], *p;
	scanf("%d %d %d %d", &N, &M, &S, &T);
	for (i = 1; i <= N; i++) scanf("%d", &(P[i]));
	for (i = 0; i < M; i++) {
		scanf("%d %d", &u, &w);
		e[i*2].v = w;
		e[i*2+1].v = u;
		e[i*2].next = adj[u];
		e[i*2+1].next = adj[w];
		adj[u] = &(e[i*2]);
		adj[w] = &(e[i*2+1]);
	}
	
	int X = P[S], Y = 0, flag[100001] = {};
	max_heap h;
	data d;
	h.size = 0;
	d.key = P[S];
	d.id = S;
	push(d, &h);
	flag[S] = 1;
	while (h.size > 0) {
		d = pop(&h);
		u = d.id;
		if (X > P[u]) {
			X = P[u];
			Y++;
		}
		for (p = adj[u]; p != NULL; p = p->next) {
			w = p->v;
			if (flag[w] == 0) {
				flag[w] = 1;
				d.key = P[w];
				d.id = w;
				push(d, &h);
			}
		}
	}
	printf("%d\n", Y);
	fflush(stdout);
	return 0;
}