Exclude subdomain from HTTPS redirect

I need to exclude a specific subdomain (sub.domain.com) from the REDIRECT TO HTTPS rule in the web.config below. How do I do that?

<rules>
<rule name="www" stopProcessing="true">
<match url=".*" />
<conditions>
<add input="{HTTP_HOST}" pattern="^www." negate="true" />
</conditions>
<action type="Redirect" url="https://www.{HTTP_HOST}{REQUEST_URI}" redirectType="Permanent" appendQueryString="false" />
</rule>
<rule name="Redirect to https" stopProcessing="true">
<match url=".*" />
<conditions>
<add input="{HTTPS}" pattern="off" ignoreCase="true" />
</conditions>
<action type="Redirect" url="https://{HTTP_HOST}{REQUEST_URI}" redirectType="Permanent" appendQueryString="false" />
</rule>
</rules>