#!/bin/python3
import sys
import itertools 
n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
s=set()
for i in range(2,len(a)+1):
   s.update(list(itertools.combinations(a,i)))
l2=[]
cp=0
for j in s:
    c=0
    for k in list(itertools.combinations(j,2)):
        if(abs(k[0]-k[1])<=1):
            c+=1
    if(c>cp):
        x=len(j)
    cp=c
print(x)