#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
d=dict()
for i in a:
    if i not in d:
        d[i]=1
    else:
        d[i]+=1
m=0
for i in d:
    temp=d[i]
    if i+1 in d:
        temp+=d[i+1]
    m=max(m,temp)
print m