[Typo3] Include loginbox on each page

[Francesco di Francia]

> <form 
> action="index.php?id=PAGE_ON_WHICH_YOU_WANT_TO_BE_AT_SUCCESSFULL_LOGIN" 

What should i insert in action parameter if i want that user, in case of 
succesful login, stays in the same page where he was when he compiled 
the login form ?