#!/bin/python

import sys


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

cnt = [0 for _ in xrange(100)]
for e in a:
    cnt[e] += 1
    
res = 0
for x in xrange(1, 100):
    res = max(res, cnt[x] + cnt[x-1])
print res