using System;
using System.Collections.Generic;
using System.Linq;
using static System.Math;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            A();
        }

        static void A()
        {
            var N = ReadInt();
            var a = ReadSplitInt();

            var dict = new Dictionary<int, int>();
            var set = new HashSet<int>();
            for (int i = 0; i < N; i++)
            {
                set.Add(a[i]);
                if (dict.ContainsKey(a[i])) dict[a[i]] += 1;
                else dict.Add(a[i], 1);
            }

            var list = set.OrderBy(x => x).ToArray();

            var max = 0;
            if (list.Length == 1) max = dict[list[0]];
            if (list.Length == 2)
            {
                max = Max(dict[list[0]], dict[list[1]]);
                if (list[1] - list[0] == 1)
                    max = dict[list[0]] + dict[list[1]];
            }

            for (int i = 2; i < list.Length; i++)
            {
                if (list[i-1] - list[i-2] == 1 && list[i] - list[i-1] == 1)
                    max = Max(max, dict[list[i]] + dict[list[i - 1]] + dict[list[i - 2]]);

                if (list[i-1] - list[i-2] == 1)
                    max = Max(max, dict[list[i]] + dict[list[i -1]]);

                max = Max(max, dict[list[i]]);
            }
            Println(max);
        }

        static List<int> ReadLines(int n)
        {
            var l = new List<int>();
            for (int i = 0; i < n; i++)
            {
                l.Add(ReadInt());
            }
            return l;
        }

        static IEnumerable<int> Range(int start, int stop)
        {
            if (start < 0 || stop < 0 || start > stop || (start <= 0 && stop <= 0))
                return new List<int>();

            return Enumerable.Range(start, stop - start);
        }

        static bool IsDigit(string str)
        {
            var i = 0;
            return int.TryParse(str, out i);
        }

        static int SumDigits(long num)
        {
            return num.ToString().Select(x => x.ToString()).Sum(int.Parse);
        }

        static int[] ToIntArray(string str)
        {
            return str.Select(x => x.ToString()).Select(int.Parse).ToArray();
        }

        static int Gcd(int a, int b) => b == 0 ? a : Gcd(b, a % b);

        static bool IsPrime(int x)
        {
            if (x <= 1 || (x != 2 && x % 2 == 0)) return false;
            if (x == 2) return true;

            for (int i = 3; i < x; i += 2)
                if (x % i == 0) return false;

            return true;
        }

        static string Read() => Console.ReadLine();
        static int ReadInt() => int.Parse(Read());
        static long ReadLong() => long.Parse(Read());

        static List<string> ReadSplit() => Read().Split().ToList();
        static List<int> ReadSplitInt() => Read().Split().Select(int.Parse).ToList();
        static List<long> ReadSplitLong() => Read().Split().Select(long.Parse).ToList();

        static void Print(object value) => Console.Write(value.ToString());
        static void Println(object value) => Console.WriteLine(value.ToString());

        static string Join<T>(IEnumerable<T> list) => string.Join("", list);
    }

    public static class MyExtensions
    {
        public static string Slice(this string str, int start = 0, int stop = 0)
        {
            if (start > str.Length || stop > str.Length || start < 0 || stop < 0)
                return "";

            if (stop == 0) stop = str.Length;
            return str.Substring(start, stop - start);
        }
    }
}

Measured memory_bytes: 24544