Problem:
Score : 300 points

Problem Statement

You are given an integer sequence of length N, a_1,a_2,...,a_N.

For each 1≤i≤N, you have three choices: add 1 to a_i, subtract 1 from a_i or do nothing.

After these operations, you select an integer X and count the number of i such that a_i=X.

Maximize this count by making optimal choices.

Constraints

1≤N≤10^5

0≤a_i<10^5 (1≤i≤N)

a_i is an integer.

Input

The input is given from Standard Input in the following format:

N
a_1 a_2 .. a_N

Output

Print the maximum possible number of i such that a_i=X.

Sample Input 1

7
3 1 4 1 5 9 2

Sample Output 1

4

For example, turn the sequence into 2,2,3,2,6,9,2 and select X=2 to obtain 4, the maximum possible count.

Sample Input 2

10
0 1 2 3 4 5 6 7 8 9

Sample Output 2

3

Sample Input 3

1
99999

Sample Output 3

1

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System.Collections.Generic;
using System.Linq;
using Console = System.Console;

namespace Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var r = Console.ReadLine().Split().Select(int.Parse).ToArray();
            var len = r.Max();
            int ret = 0;
            Dictionary<int,int> dic = new Dictionary<int, int>();
            for (int i = 0; i < N; i++)
            {
                if (!dic.ContainsKey(r[i]))
                {
                    dic.Add(r[i],1);
                }
                else
                {
                    dic[r[i]]++;
                }
            }

            for (int i = 0; i <= len; i++)
            {
                int tmpRet = 0;
                if (dic.ContainsKey(i - 1))
                {
                    tmpRet += dic[i - 1];
                }
                if (dic.ContainsKey(i))
                {
                    tmpRet += dic[i];
                }
                if (dic.ContainsKey(i + 1))
                {
                    tmpRet += dic[i + 1];
                }

                if (ret <= tmpRet)
                {
                    ret = tmpRet;
                }
            }

            Console.WriteLine(ret);
        }
        
    }
}