from collections import deque
N,M=map(int,input().split())
H=list(map(int,input().split()))
G=[[]for _ in range(N)]
for _ in range(M):
 a,b=map(int,input().split())
 a-=1
 b-=1
 G[a].append(b)
 G[b].append(a)
d=[[-1]*2 for _ in range(N)]
d[0][0]=0
q=deque()
q.append((0,0))
while q:
 v,f=q.popleft()
 for n in G[v]:
  if H[n]>H[v]:
   if f==0 and d[n][0]<d[v][f]+1:
    d[n][0]=d[v][f]+1
    q.append((n,0))
  else:
   if d[n][1]<d[v][f]+1:
    d[n][1]=d[v][f]+1
    q.append((n,1))
a=max(d[-1])
print(a+1 if a>=0 else a)