how to take the part of a string

how i can take a part of this string :

string="<ArrayOfArrayOfKeyValueOfstringstring xmlns:d1p1="http://www.w3.org/2001/XMLSchema" i:type="d1p1:base64Binary" xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/2003/10/Serialization/Arrays">0RuHA6OkPMP7myQPAR4ZDMoB8mo=</ArrayOfArrayOfKeyValueOfstringstring>";

i need to take just this part "0RuHA6OkPMP7myQPAR4ZDMoB8mo" , how can i programmaticaly divide the part i need?

its not an xml its the string the system give me back when i ask details of the telephone, i need to get only the part of the IMEI:

 Object obj = DeviceExtendedProperties.GetValue("DeviceUniqueId");
 byte[] objByte = ObjectToByteArray(obj);
 IMEI = System.Text.Encoding.UTF8.GetString(objByte, 0, objByte.Length);

this the ObjectToByteArray():

 private byte[] ObjectToByteArray(Object obj)
        {
            DataContractSerializer serializer = new DataContractSerializer(typeof(List<Dictionary<String, String>>));

            byte[] byteArr;

            using (var ms = new System.IO.MemoryStream())
            {
                serializer.WriteObject(ms, obj);
                byteArr = ms.ToArray();
            }
            return byteArr;

i cut the string using Split and Replace by this way:

 a1 = IMEI.Split(IMEIerrato, 2 ,StringSplitOptions.None);
 IMEIgiusto = a1[1].Replace("=</ArrayOfArrayOfKeyValueOfstringstring>", "");
 Debug.WriteLine("IMEI: "+IMEIgiusto);

i get this output:

IMEI: 0RuHA6OkPMP7myQPAR4ZDMoB8mo

RESOLVED