#!/bin/python

import sys


n = int(raw_input().strip())
arr = map(int,raw_input().strip().split(' '))

nums={a:0 for a in set(arr)}
for a in arr:
  nums[a]+=1
res=0  
for a in nums.keys():
  res=max(res,nums[a])
  if a+1 in nums:
    res=max(res,nums[a]+nums[a+1])
print res