[Inkscape-user] shape question

Hey folks,

I am a fairly new user of Inkscape and was wondering how I can create a square that has rounded corners on the top, but streight corners on the bottom?

So far, I've noticed there are only 3 nodes which I can use to modify my square. One of which is used to round the corners- but it does all 4. Is there a way I can only select 2 of the 4 corners to round?

Thanks- I hope this makes sense.

Patrick