#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
cnt = [0 for _ in range(max(a) + 1)]
for num in a:
    cnt[num] += 1
res = 0
for i in range(1, len(cnt)):
    res = max(res, cnt[i] + cnt[i - 1])
print(res)