from heapq import heappush, heappop
N,M,S,T = map(int,input().split())
S -= 1
T -= 1
P = list(map(int,input().split()))
l = [[] for _ in range(N)]
for _ in range(M):
    a,b = map(int,input().split())
    a -= 1
    b -= 1
    l[a].append(b)
    l[b].append(a)

st = [(-P[S],S)]
visited = [False]*N
visited[S] = True
ans = 0
x = P[S]
while st:
    pi,i = heappop(st)
    pi = -pi
    if x > pi:
        x = pi
        ans += 1
    for j in l[i]:
        if not visited[j]:
            visited[j] = True
            heappush(st,(-P[j],j))

print(ans)