using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var dataSet = new[] { 1, 1, 4, 6, 3, 3, 1, 2, 2, 2, 6, 6, 6, 7 };

        var output = GetOutput(dataSet, 3);

        Console.WriteLine($"Output: {{ {string.Join(", ", output)} }}");

    }

    public static List<int> GetOutput(int[] input, int repetitionRequirement)

    {

        var consecutiveCount = repetitionRequirement - 1;

        var output = new List<int>();

        int? repeatedNumber = null;

        for (var i = 0; i < input.Length; i++)

        {

            var number = input[i];

            if (number == repeatedNumber)

            {

                output.Add(number);

            }

            else if (i + consecutiveCount < input.Length &&

                input.Skip(i + 1).Take(consecutiveCount).All(num => num == number))

            {

                repeatedNumber = number;

                output.Add(number);

            }

            else if (repeatedNumber.HasValue)

            {

                repeatedNumber = null;

            }

        }

        return output;

    }

}