#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
from collections import Counter

dic = Counter(a)  
max_val = 0

for a in dic:
    mm = dic[a]
    mm1 = mm2 = 0
    if a-1 in dic:
        mm1 = dic[a-1] 
    if a+1 in dic:
        mm2 = dic[a+1]
    max_val = max(max_val, mm1+mm, mm2+mm)
print max_val