I=lambda:map(int,input().split())
n,m=I()
*h,=I()
*e,=eval("[],"*n)
for i in[0]*m:
 a,b=I()
 if h[a-1]<h[b-1]:a,b=b,a
 e[a-1]+=b-1,
def f(k):
 t=[~n]*n
 t[k]=0
 for i in sorted(range(n),key=lambda x:h[x]):
  for v in e[i]:t[i]=max(t[i],t[v]+1)
 return t
print(max(-1,max(map(int.__add__,f(0),f(-1)))+1))