Import into Blogger from an Atom feed

Google has recently added the import functionality to Blogger, making it very easy to migrate from any other information service to Blogger. Unfortunately, the import process rejects anything that looks like it did not come from the Blogger export feature. I did not try to nail down the very minimum that would be required for the import to work, but this is a very minimalistic Atom document that works:

<?xml version='1.0' encoding='utf-8'?>
<feed xmlns='http://www.w3.org/2005/Atom' 
      xmlns:openSearch='http://a9.com/-/spec/opensearchrss/1.0/'  
      xmlns:gd='http://schemas.google.com/g/2005'
      xmlns:thr='http://purl.org/syndication/thread/1.0'>
    <id>tag:blogger.com,1999:blog-123456789.archive</id>
    <updated>2008-11-01T00:00:00.000+01:00</updated>
    <title type='text'>Sample import file</title>
    <author>
        <name>Example.com</name>
        <uri>http://www.blogger.com/profile/12345678</uri>
        <email>noreply@blogger.com</email>
    </author>
    <generator version='7.00' uri='http://www.blogger.com'>Blogger</generator>
    <entry>
        <id>tag:blogger.com,1999:blog-123456789.post-12345678</id>
        <published>2008-11-01T00:00:00.000+01:00</published>
        <updated>2008-11-01T00:00:00.000+01:00</updated>
        <category scheme='http://schemas.google.com/g/2005#kind' 
          term='http://schemas.google.com/blogger/2008/kind#post'/>
        <category scheme='http://www.blogger.com/atom/ns#' term='CatItem'/>
        <title type='text'>Post title</title>
        <content type='html'>Post text, HTML needs to be escaped</content>
        <author>
            <name>Example.com</name>
            <uri>http://www.ioshints.info/about</uri>
            <email>noreply@blogger.com</email>
        </author>
        <thr:total>0</thr:total>
    </entry>
</feed>