import bisect
import copy
import decimal
import fractions
import heapq
import itertools
import math
import random
import sys
import time
from collections import Counter,deque,defaultdict
from functools import lru_cache,reduce
from heapq import heappush,heappop,heapify,heappushpop,_heappop_max,_heapify_max
def _heappush_max(heap,item):
    heap.append(item)
    heapq._siftdown_max(heap, 0, len(heap)-1)
def _heappushpop_max(heap, item):
    if heap and item < heap[0]:
        item, heap[0] = heap[0], item
        heapq._siftup_max(heap, 0)
    return item
from math import gcd as GCD
read=sys.stdin.read
readline=sys.stdin.readline
readlines=sys.stdin.readlines
write=sys.stdout.write
#import pypyjit
#pypyjit.set_param('max_unroll_recursion=-1')
#sys.set_int_max_str_digits(10**9)

N,M,S,T=map(int,readline().split())
S-=1;T-=1
P=list(map(int,readline().split()))
for i in range(N):
    P[i]-=1
graph=[[] for x in range(N)]
for m in range(M):
    a,b=map(int,readline().split())
    a-=1;b-=1
    graph[a].append(b)
    graph[b].append(a)
queue=[(P[S],S)]
seen=[False]*N
seen[S]=True
Y=[-1]*N
y=0
x=P[S]
while queue:
    p,a=_heappop_max(queue)
    if x>P[a]:
        x=P[a]
        y+=1
    Y[a]=y
    for b in graph[a]:
        if seen[b]:
            continue
        _heappush_max(queue,(P[b],b))
        seen[b]=True
ans=max(Y)
print(ans)