#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
ma=0
for x in range(n):
    su=0
    for y in range(n):
        if (a[y]==a[x]+1 or a[y]==a[x]):
            su=su+1
    if ma<su:
        ma=su
print ma