How to make custom sequence order in crystal report grouping..?

Question

Hai,

 I want to know how to customise the sequence of groups in the crystal report.
 In my crystal report I have groups like sales, exchange, return, and order. The order of report is first Sales,then exchange,return and last order.

 If there is only exchange and order in my bill I want to get order as the first group then second as exchange.

 To make the grouping I am passing a value say group_number from my programe (that is for sales its 1, exchange - 2, return - 3, and order - 4)

 I think I can solve this using group expert in crystal report but I tried that but did't get what actually I need,

 If any body have any idea to solve this problem please help me..

Thanks in advance,
waiting for a good answer..