#!/bin/python

import sys
from collections import defaultdict

n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
a = sorted(a)
hmap = defaultdict(lambda:0)
for i in a:
    if hmap.has_key(i-1):
        hmap[i-1]+=1
    elif hmap.has_key(i):
        hmap[i] +=1
    else:
        hmap[i] =1
print max(hmap.values())