Can i contain duplicate values in Hashset object?

hashset object in C# A HashSet object contains the non duplicate values or You can say the HashSet object is the collection of the objects that contains no duplicate elements, and whose elements are in no particular order. I can not add the item that is already exist in the HashSet object.
 
In the Following example you can see how to add the values to the HashSet object.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            HashSet<int> EmployeeIds = new HashSet<int>();
 
            // Add numbers to HashSet object 'EmployeeIds'
            EmployeeIds.Add(11);
            EmployeeIds.Add(12);
            EmployeeIds.Add(13);
            // Add again 11 to EmployeeIds
            EmployeeIds.Add(11);
 
            Console.WriteLine("Total count of the EmployeeIds= " 
                + EmployeeIds.Count);
            foreach (int i in EmployeeIds)
            {
                Console.WriteLine(i);
            }
            Console.ReadKey();
        }
    }
}

 
The above programe will produce the following output:
Total count of the EmployeesIds = 3
11
12
13