Codeigniter web.config index.php rewrite inside a subdirectory

It's for webconfig file to remove index.php

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
 <system.webServer>
   <rewrite>
     <rules>
       <rule name="Imported Rule 1" stopProcessing="true">
         <match url="^(.*)$" ignoreCase="false" />
         <conditions logicalGrouping="MatchAll">
             <add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" />
             <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />
         </conditions>
         <action type="Rewrite" url="index.php?url={R:1}" appendQueryString="true" />
         </rule>
     </rules>
   </rewrite>
 </system.webServer>
</configuration>

The above code not working for me. my folder structure as follow
httpdocs
|- admin
|--|- application
|--|- system
|--|- index.php
|--|- web.config
|
|- application
|- system
|- index.php
|- web.config
this hosted in windows hosting server. if i add $config['index_page']='index.php'; in config file under application/config/config.php. site is working but when i remove $config['index_page']=''; like this that is showing 404 page not found error.please help me out from this issue.
Thanks[/quote]