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

s -= 1; t -= 1
from heapq import *
q = [(-p[s],s)]

used = [0]*n
used[s] = 0
ans = 0
X = p[s]
while q:
    x,v = heappop(q)
    x = -x
    if X > x:
        X = x
        ans += 1
    for c in g[v]:
        if used[c] == 0:
            heappush(q,(-p[c],c))
            used[c] = 1
print(ans)