#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
maxi = 0
for i in range(1, max(a)):
    c = 0
    for elem in a:
        if(elem == i or elem == i+1):
            c += 1
    if(c > maxi and c != 0):
        maxi = c
print (maxi)