How to create a variable which takes input from user(prompt variable) in sap bo webi?

Hi All

        I got to apply Ranking to my Records in the report,in Webi for which I need to create a variable which is like a prompt requires input to be chosen.I am trying to use the Inlist() function in the variable ,but getting error. The Ranking()  functionality is disabled in my webi tool.Any other way to achive this??