#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
arr = [0]*101
for e in a:
    arr[e] += 1
_max = 0
for e in a:
    _max = max(_max, arr[e - 1] + arr[e], arr[e] + arr[e + 1])
print _max