There was another thread regarding Ricoh pin not so long ago. You can search for it.
The pin is the one at 2pm on your picture (or if you point the red alignment dot at 12pm, then it is at about 6pm). The other pin together with the three other contacts is the A pin.
I have removed the Ricoh pin from my Sigma lens so if you have any questions let me know. There is also a nice guide with pictures
here but my lens did have a different mount underneath.
Oh, and one more thing, do not loose the small ball that makes the nice click when you change the aperture ring.