import heapq
from collections import deque
from sys import stdin

N,M,S,T = map(int,stdin.readline().split())
S -= 1
T -= 1

p = list(map(int,stdin.readline().split()))

lis = [ [] for i in range(N) ]

for i in range(M):

    a,b = map(int,stdin.readline().split())
    a -= 1
    b -= 1

    lis[a].append(b)
    lis[b].append(a)

X = p[S]
Y = 0

q = [(-1*p[S],S)]
inlis = [False] * N
inlis[S] = 0

while q:

    np,v = heapq.heappop(q)
    np *= -1

    if X > np:
        X = np
        Y += 1

    for nex in lis[v]:
        if not inlis[nex]:
            inlis[nex] = True
            heapq.heappush(q,(-1*p[nex],nex))

print (Y)