#!/bin/python

import sys
from collections import Counter

def max_ones(a):
    c = Counter(a)
    ongoing_pairs = Counter()
    for i in c:
        ongoing_pairs[(i, i+1)] = c[i] + c[i+1]
    return ongoing_pairs.most_common()[0][1]

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

print max_ones(a)