#!/bin/python

import sys
from collections import OrderedDict, Counter

n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))

ac = Counter(a)
aod = OrderedDict(ac).items()



max_pairs = 0
for i in xrange(len(aod) -1):
    if (aod[i][0] + 1) == aod[i+1][0]:
        count = aod[i][1] + aod[i+1][1]
        if count > max_pairs:
            max_pairs = count

if aod[0][1] > max_pairs:
    max_pairs = aod[0][1]

if aod[len(aod)-1][1] > max_pairs:
    max_pairs = aod[len(aod)-1][1]
print max_pairs