#!/bin/python

import collections


a = raw_input()
b = raw_input()

num = map(int,b.strip().split(" "))
num.sort()

num_set = set(num)
num1 = list(num_set)

counter = collections.Counter(num)

max_c = 0

for i in range(0,len(num1)):
	if i == 0:
		max_c = counter[num1[i]]
	else:
		if num1[i]-num1[i-1]==1:
			if counter[num1[i]] + counter[num1[i-1]] > max_c:
				max_c = counter[num1[i]] + counter[num1[i-1]]
		else:
			if counter[num1[i]] > max_c:
				max_c = counter[num1[i]]

print max_c