<?xml version="1.0" encoding="utf-16"?>
<content Version="80903">
  <call commcount="3" taskcount="0">
    <property_simple key="callresult" value="busy" />
    <activity>
      <commutation index="0">
        <property_simple key="idconnection" value="1fc1410d-47f9-43b0-a685-af8334a068b8" />
        <property_simple key="totalsec" value="1" />
        <property_simple key="ivrscriptname" value="name2" />
      </commutation>
      <commutation index="1">
        <property_simple key="idconnection" value="1fc1410d-47f9-43b0-a685-af8334a068b8" />
        <property_simple key="totalsec" value="2" />
        <property_simple key="ivrscriptname" value="name1" />
      </commutation>
      <commutation index="2">
        <property_simple key="idconnection" value="adbb49de-bdab-4fc4-86dd-cdeec65b4d56" />
        <property_simple key="totalsec" value="3" />
      </commutation>
    </activity>
  </call>
</content>

var res = docXml.Descendants().Elements("commutation").Elements("property_simple").Where(c => c.Attribute("key").Value == "totalsec").Sum(c1 => Convert.ToInt32(c1.Attribute("value").Value));