Hoa to check main category of post

Hi there,

I've got a question about categories.

I need to check in list of posts what is main category, where the post is added.

My categories structure looks like below:

Main category 01
- subcategory 01
- subcategory 02

Main category 02
- subcategory 03
- subcategory 04

and I need to show not directly category, where the post is added, but category above subcategory.

So how can I check this and show in post in list view (default.main.php) by adding some short code?

I'll be very grateful for your help with this thread!
Best regards!
Adam