using System;

class Solution
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        int[] a = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);

        int r = 0, r1 = 0, r2 = 0, c = -1;
        Array.Sort(a);

        for (int i = 0; i < n; ++i)
        {
            if (a[i] == c)
            {
                ++r2;
            }
            else
            {
                if (r1 + r2 > r) r = r1 + r2;
                r1 = (a[i] == c + 1) ? r2 : 0;
                r2 = 1;
                c = a[i];
            }
        }

        if (r1 + r2 > r) r = r1 + r2;

        Console.WriteLine(r);
    }
}