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: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;

public class Program {
    public static void Main() {
        var n = int.Parse(Console.ReadLine());
        var arrs = Console
            .ReadLine()
            .Split(' ')
            .Select(s => int.Parse(s))
            .GroupBy(k => k)
            .Select(g => g.Count())
            .ToArray();

        int score;
        if (arrs.Length <= 2) {
            score =  arrs.Sum();
        } else {
            var counts = new int[n - 2];

            for (int i = 0; i < n - 3; i++) {
                counts[i] = arrs[i] + arrs[i + 1] + arrs[i + 2];
            }
            score = counts.Max();
        }

        Console.WriteLine(score);
    }
}