How to Track App Download by adding CID as a parameter in iTunes URL?

Hi,

I want to track my application download by passing CID (Campign ID) as a parameter in iTunes URL. The delegate method which i am using to fetch the parameter is:

- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url sourceApplication:(NSString *)sourceApplication annotation:(id)annotation

Can you please help me how to track campign ID so that i can save it?

Please help

Thanks.