#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
lst = [0] * 101
count = 0
for i in a:
    lst[i] += 1
for i in range(1,100):
    count = max(count, lst[i] + lst[i+1])
print (count)