#!/bin/python

import sys
from collections import Counter


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
c = Counter(a)
max_count = 0
for k, v in c.items():
    if c[k] + c[k+1] > max_count:
        max_count = c[k] + c[k+1]
print(max_count)