using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {   
  

    static void Main(String[] args) {
        int n = Convert.ToInt32(Console.ReadLine());
        string[] a_temp = Console.ReadLine().Split(' ');
        int[] a = Array.ConvertAll(a_temp,Int32.Parse);       
        
        
        // number of appearences        
        var appear = new Dictionary<int, int>();
        foreach (var number in a)
        {
            if (appear.ContainsKey(number))
            {
                appear[number]++;    
            }
            else
            {
                appear.Add(number, 1);
            }
        }
        
        // sort keys
        var keys = appear.Keys.ToList();       
        keys.Sort();
        
        // greedy        
        var bestNumber = 0;       
      
        for(int i = 0; i < 100; i++)
        {
            var firstOfThree = appear.ContainsKey(i) ? appear[i] :0;
            var secondOfThree = appear.ContainsKey(i+1) ? appear[i+1] :0;           
            var sumOfThree = firstOfThree  + secondOfThree;
            
            if (sumOfThree > bestNumber)
            {                
                bestNumber = sumOfThree;                
            }        
                
        }
        
        // ouput
        Console.WriteLine(bestNumber);       
    }
}