n,*a=map(int,open(0).read().split())
if n<2:exit(print(n))
r=c=2;d=a[1]-a[0]
for i in range(1,n-1):c+=1 if a[i+1]-a[i]==d else 0;c=r=max(r,c) if a[i+1]-a[i]==d else (2,r:=r);d=a[i+1]-a[i] if c==2 else d
print(r)