After file upload, can I decrement a counter ?

I have a page on a web site from which a customer can upload a file to the
server. The code contains

<code>
<form id="Form1" method="post" enctype="multipart/form-data" runat="server">

<input id="submit1" type="submit" value="Upload" runat="server" name="submit1" />
</code>

What I should like to be able to do, is to decrement a counter after the upload
has taken place.

Is there a signal somewhere in .vb that enable me to write n=n-1 after
the signal has appeared ?
...