n,m=map(int,input().split())
h=list(map(int,input().split()))
rev=[0]*n
for i in range(n):
    rev[h[i]-1]=i
G=[[] for _ in range(n)]
for i in range(m):
    a,b=map(int,input().split())
    G[a-1].append(b-1)
    G[b-1].append(a-1)
d1,d2=[-1e9]*n,[-1e9]*n
d1[0]=0
d2[n-1]=0

def dp(d):
    for i in rev:
        for j in G[i]:
            if h[i]<h[j]:
                d[j]=max(d[j],d[i]+1)
    pass
                
dp(d1)
dp(d2)

ans=-1e9
for i in range(n):
    ans=max(ans,d1[i]+d2[i])
if ans<0:
    ans=-2
print(ans+1)