#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
f=[0]*1005
for i in set(a):
    f[i]=a.count(i)
m=max(a)
s=[]
for i in xrange(1,m):
    s.append(f[i]+f[i+1])
print max(s)