[Typo3] How to get parent id of current page?

[Pawe³ Stanis³awczuk]

Hello,

How to get parent ID of current page? i.e we are in main1/sub3

root
--main1(uid:1)
----sub1(uid:3)
----sub2(uid:4)
----sub3(uid:5)
--main2(uid:2)
----sub1(uid:6)
...
..
.

how can I get the main1 UID while being in sub3 ?
I'm creating a php function in 'example_callfunctions.php' so I'm searching 
a variable some sort. I'm getting my UID of current page (ie sub3's UID) 
with this:

.intval($GLOBALS['TSFE']->id).

works great, now what to do to receive parent ID (ie main1's UID) ?

greetz,
Pawe³ Stanis³awczuk