using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var qpr = new List<string>();

        var accoUrl = "griekenland/kreta/analipsi/stella-palace-resort-en-spa?someparam=x&";

        qpr.Add("mystring=1");

        qpr.Add("myotherstring=2");

        qpr.Add("ourstring=3");

        string q = string.Join("&", qpr).ToLower();

        if (accoUrl.EndsWith("?") || accoUrl.EndsWith("&"))

        {

            //Console.WriteLine($"{accoUrl}{q}");

        }

        /*string sep  = "?";

        if (accoUrl.IndexOf('?') > 0)

        {

            sep = "&";

        }*/

        string sep = accoUrl.Contains("?") ? "&" : "?";

        Console.WriteLine($"{accoUrl}{sep}{q}");

    }

}