How to replace the Selenium's storeEval variable everytime we run the program?

Hi guys,
I am using selenium RC to run an automated test. I wish to generate random 5 digit on a button click using following code.                  String random = selenium.GetEval("Math.floor (Math.random() * 99999)"); selenium.Type("id=name",random);
but the problem occurs when i click the button twice. For example, the first attempt will be 12345, second try will be 1234567894 perhaps. Third try will be 123451234512345.  Is there any way to replace the original value when next try ? Thank in advance. ...