R=range
J=lambda:list(map(int,input().split()))
N,M=J()
H=[0]+J()
E=[[]for i in R(N+1)]
for m in R(M):u,v=J();E[u]+=[v];E[v]+=[u]
W=N*3
D=[0,0]+[-W]*N
for h,i in sorted((H[i],i)for i in R(1,N+1)):
	for j in E[i]:
		if h<H[j]:D[j]=max(D[j],D[i]+1)
for h,i in sorted((-H[i],i)for i in R(1,N+1)):
	for j in E[i]:
		if H[j]<-h:D[j]=max(D[j],D[i]+1)
print(max(-1,D[N]+1))