#int(input())
#map(int, input().split())
#list(map(int, input().split()))

N, M, S, T = map(int, input().split())
p = list(map(int, input().split()))

to = [[] for i in range(N)]
for i in range(M):
    a, b = map(int, input().split())
    to[a-1].append(b-1)
    to[b-1].append(a-1)

S -= 1
T -= 1

import heapq
q = [(-p[S], S)]
X = p[S]
a = []
v = [0] * N
v[S] = 1

heapq.heapify(q)

while q:
    t, x = heapq.heappop(q)
    t *= -1
    qq = [x]
    a.append(t)
    # if x == T:
    #     break

    while qq:
        u = qq.pop()
        for y in to[u]:
            if v[y] == 1:
                continue
            if p[y] >= t:
                qq.append(y)
            else:
                heapq.heappush(q, (-p[y], y))
            v[y] = 1

ans = 0
for i in range(len(a)-1):
    if a[i] > a[i+1]:
        ans += 1

print(ans)