#!/bin/python

import sys
from collections import Counter

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

numbers = list(sorted(set(a)))
counts = Counter(a)

tups = []
for i in range(len(numbers)-1):
    if numbers[i+1] - numbers[i] == 1:
        tups.append((numbers[i], numbers[i+1]))

most_common,num_most_common = counts.most_common(1)[0]
maxcount = num_most_common
for tup in tups:
    count = counts[tup[0]] + counts[tup[1]]
    if count > maxcount:
        maxcount = count

print maxcount