#!/bin/python

import sys


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

counts = {}
for el in a:
    if counts.get(el):
        counts[el] += 1
    else:
        counts[el] = 1
list_counts = []
for k, v in counts.iteritems():
    list_counts.append([k, v])
sorted_counts = sorted(list_counts, key=lambda x: x[0])

max_len = 0
prev = sorted_counts[0]
max_count = sorted_counts[0][1]

for el in sorted_counts[1:]:
    if max_count < el[1]:
        max_count = el[1]
    if abs(el[0] - prev[0]) == 1:
        if prev[1] + el[1] > max_len:
            max_len = prev[1] + el[1]
    prev = el

if max_len < max_count:
    max_len = max_count

print max_len