using System;

using System.Collections.Generic;

public class Program

{

    public enum InvoiceIssue {

        NotAnInvoice,

        PageMissing,

        PageOutOfOrder

    }

    public static void Main()

    {

        List<InvoiceIssue> invoiceIssues = new List<InvoiceIssue> { InvoiceIssue.NotAnInvoice, InvoiceIssue.PageMissing };

        Console.WriteLine(string.Join(",", invoiceIssues));

        invoiceIssues = new List<InvoiceIssue> {};      

        Console.WriteLine(string.Join(",", invoiceIssues));

        invoiceIssues = new List<InvoiceIssue> { InvoiceIssue.PageOutOfOrder };     

        Console.WriteLine(string.Join(",", invoiceIssues));

    }

}