Bex variable :problem

Hi Guys,

In my bex report i ave two date fields on the selection screen.They get input from the users.Now my requirement is that i have to make any one of the fileds among these 2 mandatory.

If user gives input to both fields then a pop comes sayin "fill in any one".which is working fine......and if user leaves both blank then the same pop shud come saying "fill up atleast one ".....i cannot make this work....any suggestions?

have any one worked on this type of requirement..........i need to write the code in i step 3....kindly help...

tina