from collections import deque
N,M,S,T = map(int,input().split())
S -= 1
T -= 1
P = list(map(int,input().split()))
l = [[] for _ in range(N)]
for _ in range(M):
    a,b = map(int,input().split())
    a -= 1
    b -= 1
    l[a].append(b)
    l[b].append(a)

st = deque([(S,P[S],0)])
X,Y = 0,0
while st:
    i,x,y = st.popleft()
    if i == T:
        X,Y = x,y
        break
    for j in l[i]:
        if P[j] < x:
            x = P[j]
            y += 1
        st.append((j,x,y))

st = deque([(T,X,Y)])
visited = [False]*N
while st:
    i,x,y = st.popleft()
    Y = max(Y,y)
    for j in l[i]:
        if not visited[j]:
            visited[j] = True
            if P[j] < x:
                x = P[j]
                y += 1
            st.append((j,x,y))
print(Y)