#!/bin/python

import sys
from collections import *

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

c=Counter(a)
k=sorted(c.keys())
mx=c[k[0]]

if 1==1:
    for i in range(len(k)-1):
        mx=max(mx, c[k[i+1]])
        if abs(k[i+1]-k[i])<=1:
            mx=max(mx, c[k[i+1]]+c[k[i]])
    
print mx