User prompt query

I have a query that has a dialog box that opens for the user to enter the data criteria. It is not fancy or complicated just:
[Enter CMS number]

However now I need to be able if they want multiple choices. For example they want more than one number they would enter
850 or 851 in the dialog box. This doesn't work the way I have it now. How do I allow for this?

Thanks .... texasalynn