buy 1 piece and get 30% discount for next 1 piece with same item.

Hi,     I have case such as : If a customer buy Item A 1@ , he/she will pay full price but if a customer buy item A 2@ , he/she will get discount 30% for the next 1@.     Example : Item A ,unit price = 100$                     1. If a customer buy item A 1@ ,he/she will pay 100$.                     2. If a customer buy Item A 2@, he/she will pay 200-(100*30%) = 170$.                     3. If a customer buy Item A 3@, he/she will pay 300-(100*30%) = 270$.                     4. If a customer buy Item A 4@, he/she will pay 400-(200*30%) = 340$. etc.     Can anyone advise me ,how to setup advance pricing on E1 9.2? Regards,