#!/bin/python

import sys


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

NUMS = {}
for each in a:
    NUMS[each] = 0
for each in a:
    NUMS[each] += 1

k = sorted(NUMS.keys())
# print k
maxi = 0
for i in range(len(k)-1):
    if k[i] == k[i+1] - 1:
        # print "now ", k[i],maxi,
        maxi = max(maxi, NUMS[k[i]] + NUMS[k[i+1]])
        # print maxi
    else:
        # print "NOPE", k[i], maxi,
        maxi = max(maxi, NUMS[k[i]])
        # print maxi
        
        
print max(maxi, NUMS[k[-1]])