#!/bin/ruby

n = gets.strip.to_i
a = gets.strip
a = a.split(' ').map(&:to_i)

num_count = Hash.new(0)

a.each do |num|    
    num_count[num] += 1
end

max = 0
num_count.each_pair do |k, v|
    count = v + num_count[k + 1]
    max = count if count > max
end

puts max