from heapq import heappop, heappush
n, m, s, t = map(int, input().split())
s -= 1
t -= 1
p = list(map(int, input().split()))
to = [[] for _ in range(n)]
for _ in range(m):
    a, b = map(int, input().split())
    a -= 1
    b -= 1
    to[a].append(b)
    to[b].append(a)
added = [False] * n
added[s] = True
q = [(-p[s], s)]
x, y = p[s], 0
while q:
    pi, i = heappop(q)
    pi = -pi
    if pi < x:
        x = pi
        y += 1
    for v in to[i]:
        if added[v]:
            continue
        added[v] = True
        heappush(q, (-p[v], v))
print(y)