using System;

public class Program

{

    public static void Main()

    {

        int M = 7;

        int[] A = new int[9] { 1, 2, 3, 3, 5, 5, 6, 6, 6 };

​

        int N = A.Length;

        int[] count = new int[N];//int[] count = new int[M + 1];

​

        for (int i = 0; (i < N && A[i]<M); i++)//for (int i = 0; i <= M; i++)

        {               

            count[A[i]] = count[A[i]] + 1; //count[i] = 0;

        }

​

        int maxOccurence = 1;

        int index = -1;

​

        for (int i = 0, j = 0; i < N && j <= M; i++, j++)

        {

            if (count[j] > 0)

            {

                int tmp = count[A[i]];

​

                if (tmp > maxOccurence)

                {

                    maxOccurence = tmp;

                    index = i;

                }

                count[j] = tmp + 1;

            }

            else

            {

                count[j] = 1;

            }

        }

        var test = A[index];        

        Console.Write(test);//added this

    }   

}