yast command not found

Hi all,

I just installed a OpenSUSE 13.1
Now i want to install Apache server in this system,
but when i type a command yast -i apache2
it said -bash: yast: command not found
i remember yast should be including in OpenSUSE ?
So i'm wonder why this message appearing?
May i know how can i use yast in openSUSE 13?
Thank all.

Brgds/Brandon Chau