using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Collections;

namespace ConsoleApplication1
{
    class hr44_1
    {
        static void Main(string[] args)
        {
            //Console.SetIn(new StreamReader(@"D:\Sergey\Code\1.txt"));

            int n = int.Parse(Console.ReadLine());
            var a = new SortedList<int, int>(n);

            string[] strParams = Console.ReadLine().Split(new char[] { ' ' });

            for (int i = 0; i < n; i++)
            {
                int k = int.Parse(strParams[i]);
                int v;
                if (!a.TryGetValue(k, out v))
                {
                    v = 0;
                }
                a[k] = v + 1;
            }

            int p = -1, c = 0, m = 0;
            //for (int i = 1; i < a.Count; i++)
            foreach(var kv in a) 
            {
                if (p == -1)
                {
                    c = kv.Value;
                }
                else
                {
                    if (Math.Abs(p - kv.Key) == 1)
                    {
                        c = a[p] + kv.Value;
                    }
                    else
                    {
                        c = kv.Value;
                    }
                }
                p = kv.Key;
                if (c > m)
                    m = c;
            }


            Console.WriteLine(m);
        } // Main
    }
}