using System;

using System.Xml;

using System.IO;

​

public class Program

{

    public static void Main()

    {

        var reportIdToAcknowledge = "";

         var reportListResultXml = "<?xml version=\"1.0\"?><GetReportListResponse xmlns=\"http://mws.amazonaws.com/doc/2009-01-01/\"><GetReportListResult><HasNext>false</HasNext><ReportInfo><ReportType>_GET_FLAT_FILE_ORDERS_DATA_</ReportType>"+

      "<Acknowledged>false</Acknowledged><ReportId>11656</ReportId><ReportRequestId>11377</ReportRequestId><AvailableDate>2018-10-10T15:10:42+00:00</AvailableDate>"+

             "</ReportInfo></GetReportListResult><ResponseMetadata><RequestId>43321dc0-df4f-4393-9ad2-2b65d023260e</RequestId></ResponseMetadata></GetReportListResponse>";

            using (var reader = new XmlTextReader(new StringReader(reportListResultXml)))

            {

                reader.Namespaces = false;

​

                if (reader.ReadToDescendant("Acknowledged"))

                {

                    reader.Read();

                    if(!Boolean.Parse(reader.Value))

                    {

                        reader.ReadToFollowing("ReportId");

                         reader.Read();

                        reportIdToAcknowledge = reader.Value;

                    }

                }

​

                Console.WriteLine(reportIdToAcknowledge);

            }

    }

}