#!/bin/python

import sys
n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
a.sort()
max=0
i=0
while(i<len(a)):
    count=1
    while(i+1<len(a) and a[i]==a[i+1]):
        count+=1
        i+=1
    if i+1<len(a) and a[i]+1==a[i+1]:
        count+=1
        i+=1
        while(i+1<len(a) and a[i]==a[i+1]):
            i+=1
            count+=1
    if count>max:
        max=count
    i+=1
print max