#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
arr = []
for i in range(100):
    arr.append(0)
for i in a:
    arr[i] += 1
total = 0
for i in range(99):
    if arr[i] + arr[i+1] > total:
        total = arr[i] + arr[i+1]
print(total)