#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
a.sort()
max = 0
cnt = 0
prev = -1000
for i in a:
    if i-prev > 1:
        if cnt > max: max = cnt
        cnt = 0
        prev = i
    else:
        if cnt == 0:
            cnt = 2
        else:
            cnt +=1
if cnt > max: max = cnt
print max