#!/bin/python3

import sys


n = int(raw_input().strip())
a = [int(a_temp) for a_temp in raw_input().strip().split(' ')]

cnt=[0]*100
for ia in a:
    cnt[ia] += 1

maxcnt=0
for i in xrange(2,100):
    if cnt[i]+cnt[i-1]>maxcnt:
        maxcnt=cnt[i]+cnt[i-1]
print maxcnt