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-csc 3.5.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.ExceptionServices;
using System.Runtime.InteropServices;
using System.Text;

namespace AtCoder
{
	class Program
	{
		static void Main(string[] args)
		{
			Question.Exec();
		}
	}

	public static class Question
	{
		public static void Exec()
		{
			int n = int.Parse(Console.ReadLine());
			var a = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToArray();
			var dict = new Dictionary<int, int>();

			for (var i = 0; i < n; ++i) {
				for (var j = -1; j <= 1; ++j) {
					int b = a[i] + 1;
					if (dict.ContainsKey(b)) {
						++dict[b];
					} else {
						dict.Add(b, 1);
					}
				}
			}

			int max = dict.Values.Max();

			Console.WriteLine($"{max}");
			Console.ReadKey();
		}
	}
}