How to limit the values in input box

[#1]

Hi,

I have an input box with v_ReportLimit for entering records limit manually , I am trying to disply error message for that taking  below condition

IsNum($) and $ >= 0 and $ <= 500000 in custom option of constraints tab ,

So while selecting any value between 0 to 500000 it is showing report but my issue is if i don't select any value in the input box it has to disply default 500000 records  in the report

Is it possible, can any one help me to get this ..

Thanks,

Ankitha

[tresB]

Goto Constraints tab, Input Constraints->Custom (Write your expression), error message