#!/bin/python
import sys

n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))[:n]
maxnum=0
for i in a:
    numbers=a.count(i)
    nuplus1=a.count(i+1)
    if maxnum<numbers+nuplus1:
        maxnum=numbers+nuplus1
print maxnum