#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
a.sort()
m=0
t=0
f=0
l=0
v=a[0]
for i in a:
    if v!=i:
        if l==v-1 and m<t+f:
            m=t+f
        if f>m:
            m=f
        l=v
        t=f
        f=0
        v=i
    if i==v:
        f+=1
if l==v-1 and m<t+f:
    m=t+f
if f>m:
    m=f
print(m)