using System;

public class Program

{

    public static void Main()

    {

        var theHashSet1 = new System.Collections.Generic.HashSet<int>();

        var theHashSet2 = new System.Collections.Generic.HashSet<int>();

​

        // bool Add(T item)

        theHashSet1.Add(1);

        theHashSet1.Add(2);

        theHashSet1.Add(3);

​

        theHashSet2.Add(3);

        theHashSet2.Add(5);

        theHashSet2.Add(8);

        theHashSet2.Add(13);

​

        Console.WriteLine("First Hashset:");

        foreach(var value in theHashSet1)

        {

            Console.WriteLine($"   {value}");

        }

​

        Console.WriteLine("Second Hashset:");

        foreach(var value in theHashSet2) 

        {

            Console.WriteLine($"   {value}");

        }

​

        theHashSet1.UnionWith(theHashSet2);

        Console.WriteLine("First Hashset union with second Hashset:");

        foreach(var value in theHashSet1) 

​

        {

            Console.WriteLine($"   {value}");

        }       

    }

}