using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

    IEnumerable<string> uno = ["a", "b", "c"];

    IEnumerable<string> dos = ["c", "d", "e"];

    var tresUnion = uno.Union(dos);

    var tresConcat = uno.Concat(dos);

    Console.WriteLine($"Union count: {tresUnion.Count()}");

    Console.WriteLine($"Concat count: {tresConcat.Count()}");

    }

}