getting size of mail with attachments

how should i write a procmail script that will check the size of the
mail
and report(by email) if it is more than 1000 bytes.

.procmailrc
:0:
* if the size of the mail is more than 1000 bytes then it should mail
to-----?
! admin(_at_)somewhere(_dot_)com with subject "large mail"
-----?
:0C
$DEFAULT

How should i write the above two line in .procmailrc script.