#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
count = {}
for i in a:
    count[i] = count.get(i,0)+1
    if i > 0:
        count[i-1] = count.get(i-1,0)+1
max_count = 0
for i,c in count.items():
    if max_count < c : max_count=c
        
print(max_count)