#!/bin/python3

import sys
from collections import Counter, defaultdict, deque

N = int(input().strip())
A = [int(a_temp) for a_temp in input().strip().split(' ')]

Ac = Counter(A)
ans = 0

for a, c in Ac.items():
    ans = max(ans, c + Ac[a-1], c + Ac[a+1])
    
print(ans)