#!/bin/python

import sys

n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))

max_counts = 0
cnts = dict()
for i in a:
    if i not in cnts:
        cnts[i] = 1
    else:
        cnts[i] += 1

for i in cnts:
    if i+1 in cnts:
        if max_counts < cnts[i] + cnts[i+1]:
            max_counts = cnts[i] + cnts[i+1]
    elif max_counts < cnts[i]:
        max_counts = cnts[i]            
            
print max_counts