#!/bin/python



import sys


def solution(L):
	D = {}
	M = []
	for x in L:
		if x in D:
			D[x] += 1
		else:
			M.append(x)
			D[x] = 1

	i = 0
	j = len(M)
	result = 2

	while i < j-1:
		if (M[i+1] - M[i]) <= 1:
			total = D[M[i]] + D[M[i+1]]
			if total > result:
				result = total
		i += 1

	for x in D:
		if D[x] > result:
			result = D[x]
	return result

	


if __name__ == "__main__":
	N = int(raw_input().strip())
	L = map(int, raw_input().strip().split(' '))
	L = sorted (L)
	print solution(L)