import heapq

n, m, s, t = map(int, input().split())
s -= 1
t -= 1
p = [int(i) for i in input().split()]
e = [[] for _ in range(n)]
for _ in range(m):
    a, b = [int(i) - 1 for i in input().split()]
    e[a].append(b)
    e[b].append(a)

used = [False] * n
used[s] = True
q = [(-p[s], s)]
min_p = 10**10
ans = -1
while q:
    i, ind = heapq.heappop(q)
    i *= -1
    if i < min_p:
        min_p = i
        ans += 1
    for j in e[ind]:
        if not used[j]:
            used[j] = True
            heapq.heappush(q, (-p[j], j))
print(ans)