from collections import deque

N,M=map(int,input().split())
H=[0]+list(map(int,input().split()))

E=[[] for i in range(N+1)]
for i in range(M):
    a,b=map(int,input().split())
    E[a].append(b)
    E[b].append(a)

def bfs(x):
    Q=[x]
    D=[-1]*(N+9)
    Q=deque([x])
    D[x]=0
    while Q:
        x=Q.popleft()
        for to in E[x]:
            if H[to]>H[x] and D[to]<D[x]+1:
                D[to]=D[x]+1
                Q.append(to)
    return D

D1=bfs(1)
D2=bfs(N)
ANS=-2
for i in range(N+1):
    if D1[i]>=0 and D2[i]>=0:
        ANS=max(ANS,D1[i]+D2[i])

print(ANS+1)