using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {

    static void Main(String[] args) {
        Solve(Console.In, Console.Out);
    }
    
    public static void Solve(TextReader input, TextWriter output)
    {
        var n = Convert.ToInt32(input.ReadLine());
        var a = input.ReadLine().Split(' ').Select(int.Parse).ToArray();
        var d = a.GroupBy(g => g).ToDictionary(k => k.Key, g => g.Count());
        var result = 0;
        int q;
        d.TryGetValue(0, out q);
        int w;
        for (int i = 1; i < 100; ++i) {
            d.TryGetValue(i, out w);
            if (q + w > result)
                result = q + w;
            q = w;
        }
        output.WriteLine(result);
    }
}