How to get maximum value of a field from an Indexed file in solr

I have indexed an XML file in solr, which  looks like:

<doc>
<str name="body">ABC</str>
<str name="contentid">282307</str>
<str name="docuid">121422</str>
</doc>
<doc>
<str name="body">MNO</str>
<str name="contentid">272307</str>
<str name="docuid">188422</str>
</doc>

this file has around 100000 documents. what is the way to get maximum value from the field value "contentid" parsing the whole file.