using System;

using System.Collections.Generic;                   

public class Program

{

    public static void Main()

    {

        HashSet<int> set1 = new HashSet<int>() {1, 2, 3};

        HashSet<int> set2 = new HashSet<int>() {2, 3, 4};

        set1.Add(4);

        HashSet<int> union = new HashSet<int>(set1);

        union.UnionWith(set2);

        HashSet<int> intersection = new HashSet<int>(set1);

        intersection.IntersectWith(set2);

        Console.WriteLine("Obedinenie: ");

        foreach(int i in union)

        {

            Console.Write(i + " ");

        }

        Console.WriteLine();

        Console.WriteLine("Sechenie: ");

        foreach (int i in intersection)

        {

            Console.Write(i + " ");

        }

        Console.WriteLine();

    }

}