using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        //int[] a = {3,8,2,3,3,2};

        //int[] a = {7,1,2,8,2};

        //int[] a = {3,1,4,1,5};

        int[] a = {5,5,5,5,5};

        Console.WriteLine(LargestNumberOccur(a));

    }

    public static int LargestNumberOccur(int[] a)

    {

        int result = 0;

        Dictionary<int, int> dict = new Dictionary<int, int>();

        HashSet<int> hashSet = new HashSet<int>();

        for (int i = 0; i < a.Length; i++) {

            if (dict.ContainsKey(a[i])) {

                dict[a[i]]++;

                if (dict[a[i]] == a[i]) {

                    hashSet.Add(a[i]);

                } else if (dict[a[i]] > a[i]) {

                    hashSet.Remove(a[i]);

                }

            } else {

                dict.Add(a[i], 1);

            }

        }

        foreach (int item in hashSet) {

            result = Math.Max(result, item);

        }

        return result;

    }

}