#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
d = {}
for i in a:
    if i not in d:
        d[i] = 1
    else:
        d[i] += 1
m = 0

for i in d:
    x = 0
    if(i-1 in d):
        x = d[i-1]
    m = max(m,d[i]+x)
print(m)