#!/bin/python3

n=int(input())
a=input().split()
for i in range(len(a)):
    a[i]=int(a[i])
a.sort()
c=0
d=0
max=0
#print(a)
for i in range(len(a)-1):
    if a[i]==a[i+1]:
        c+=1  
        #print('s')
        #print(c)
    if a[i]+1==a[i+1]:
        if d==0:
            d=1
            c+=1
        else:
            d=0
            c=0
            i=a.index(a[i])
    if a[i]+1<a[i+1]:
        d=0
        c=0
        i=a.index(a[i])
        
    if max<=c:
        max=c
    #print(max)
print(max+1)