#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
index=[0]*(100)
max_sum=0
for i in range(0,n):
    index[a[i]]=index[a[i]]+1
for i in range(1,100):
    if(index[i]+index[i-1]>max_sum):
        max_sum=index[i]+index[i-1]
print(max_sum)