import sys
input = sys.stdin.readline
from heapq import *
from collections import defaultdict
class Graph:
  def __init__(self, N, M=-1):
    self.V = N
    if M>=0: self.E = M
    self.edge = [[] for _ in range(self.V)]
    self.edge_rev = [[] for _ in range(self.V)]
    self.order = []
    self.to = [0]*self.V
    self.visited = [False]*self.V
    self.dp = [0]*self.V

  def add_edges(self, ind=1, bi=False, rev=False):
    for i in range(self.E):
      a,b = map(int, input().split())
      a -= ind; b -= ind
      self.edge[a].append(b)
      if rev: self.edge_rev[b].append(a)
      if not bi: self.to[b] += 1
      if bi: self.edge[b].append(a)

  def add_edge(self, a, b, dist=-1, bi=False, rev=False):
    if dist>=0:
      self.edge[a].append((dist, b))
      if rev: self.edge_rev[b].append((dist, a))
      if bi: self.edge[b].append((dist, a))
    else:
      self.edge[a].append(b)
      if rev: self.edge_rev[b].append(a)
      if bi: self.edge[b].append(a)
    if not bi: self.to[b] += 1

  def bfs(self, start):
    self.visited[start] = True
    d = [(-P[start], start)]
    heapify(d)
    dic = defaultdict(lambda: False)
    ans = 0
    while len(d)>0:
      p,v = heappop(d)
      for w in self.edge[v]:
        if not self.visited[w]:
          if P[w]<-p:
            if dic[P[w]]==False:
              ans += 1
              dic[P[w]] = True
          else: P[w] = -p
          self.visited[w] = True
          heappush(d, (-P[w],w))
    return ans

N, M, S, T = map(int, input().split())
P = list(map(int, input().split()))
G = Graph(N,M)
G.add_edges(bi=True)
print(G.bfs(S-1))