import sys
readline = sys.stdin.readline
from heapq import *

N, M, S, T = map(int, readline().split())
S, T = S - 1, T - 1
P = list(map(int, readline().split()))
G = [[] for i in range(N)]
for i in range(M):
    A, B = map(int, readline().split())
    A, B = A - 1, B - 1
    G[A].append(B)
    G[B].append(A)

Q = []
Q.append((-P[S], S))
ans = -1
now = 10 ** 18
seen = [0] * N
while Q:
    c, u = heappop(Q)
    c = -c
    if seen[u]:
        continue
    seen[u] = 1
    if c < now:
        ans += 1
        now = c
        if u == T:
            break
    for v in G[u]:
        if seen[v]:
            continue
        heappush(Q, (-P[v], v))

print(ans)