using System;

using System.Linq;

using System.Collections.Generic;

​

​

public class Program

{

    public static void Main()

    {

        List<uint> numbers = new List<uint> { 4, 2, 2, 2, 2, 7};

        var Max_Elements_Count = 4;

        var result1 = numbers.GroupBy(p => p)

                            .Where(x => x.Count() == Max_Elements_Count)

                            .Select(x => x.Key).ToList();   

        var result2 = numbers.GroupBy(p => p, (k, group) =>  new { Key = k, Element_Count = group.Count() })

                             .Where(x => x.Element_Count == Max_Elements_Count).ToList();

        var result3 = (from n in numbers

                      group n by n into groupList

                      where  groupList.Count() == Max_Elements_Count

                      select groupList.Key).ToList();

​

​

        Console.WriteLine(result1[0]);

        Console.WriteLine(result2[0].Key);

        Console.WriteLine(result3[0]);

    }

}