XPath to get the element with the highest ID

XML Source:

<documents>
    <document>
        <id>3</id>
    </document>
    <document>
        <id>7</id>
    </document>
    <document>
        <id>1</id>
    </document>
</documents>

I need the document-element with the highest value in its id-element (so <document><id>7</id></document> in the example). I can't change the C# code, it is XMLDocument.SelectSingleNode(...), I only can modify the XPath used.

Is there something like documents/document[id=max(id)] or like order by id descending to get it?