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);
        Array.Sort(a);
        
        var answer = 0;
        var tempMax = 0;
        int? startNum = null;
        for (int i = 1; i < n; i++){
            if (a[i] - a[i - 1] <= 1){
                if (startNum != null){
                    if (a[i] - startNum <= 1){
                        tempMax++;
                    }
                    else{
                        if (answer < tempMax){
                            answer = tempMax;
                        }
                        tempMax = 0; 
                        startNum = null;
                    }
                }
                else{
                    startNum = a[i - 1];
                    tempMax++;
                }                
            }
            if (a[i] - a[i - 1] > 1){
                if (tempMax > answer){
                    answer = tempMax;
                }
                tempMax = 0;
                startNum = null;                
            }               
            
        }
        if (tempMax > answer){
                    answer = tempMax;
                }
        
        
        Console.WriteLine(answer+1);
    }
}