Arrays/ Task - 9 Frequent Number

using System;
class FrequentNumber
{
    static void Main()
    {
        int[] equalNum = { 4, 1, 1, 4, 2, 3, 4, 4, 1, 2, 4, 9, 3 };
        int[] counter=new int[equalNum.Length];
        int secondCounter = 0;
        int frequentNum = 0;
        for (int index = 0; index < equalNum.Length-1; index++)
        {
            counter[index] = 1;
            for (int check = 1; check < equalNum.Length; check++)
            {
                if(equalNum[index] == equalNum[check])
                {
                    counter[index] += 1;

                }
                if (counter[index] > secondCounter)
                {
                    secondCounter = counter[index];
                    frequentNum = equalNum[index];
                }
            }
        }
        Array.Sort(counter);
        Console.WriteLine(counter[counter.Length-1]+ " "+ frequentNum);

    }
}