#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
from collections import Counter
counter = Counter(a)
result = 0
for k, v in counter.items():
    tmp = v
    tmp1, tmp2 = 0, 0
    if k-1 in counter:
        tmp1 = counter[k-1]
    if k+1 in counter:
        tmp2 = counter[k+1]
    tmp += max(tmp1, tmp2)
    if tmp > result:
        result = tmp
print(result)