using System;

public class Program

{

    public static string PetNames(params string[] pets)

    {

        if (pets.Length == 0)

            return "You have no pets. :(";

        if (pets.Length == 1)

            return pets[0];

        if (pets.Length == 2)

            return $"{pets[0]} and {pets[1]}";

        var petNames = "";

        foreach(var pet in pets)

        {

            if (petNames != "")

                petNames += ", ";

            if (pet == pets[pets.Length-1])

                petNames += "and ";

            petNames += pet;

        }

        return petNames;

    }

    public static void Main()

    {

        var petNames = PetNames();

        Console.WriteLine(petNames);

        petNames = PetNames("Nyx");

        Console.WriteLine(petNames);

        petNames = PetNames("Nyx", "Mocha");

        Console.WriteLine(petNames);

        petNames = PetNames("Nyx", "Mocha", "Thunder", "Malmo");

        Console.WriteLine(petNames);

    }

}