Workflow with counters

Hi,

Here is my scenario:

1.        When a new item is created on the "Product Number Request" list, the workflow would start
2.       The workflow would take the value of "NextNumber" from the "Counter" list and assign to a variable (for example, "Product_var").
3.       Then the workflow would assign the value of that variable ("Product_var") to "Product Number" in the newly created item in the "Product Number Request" list
4.       Finally, the workflow would take the value of "Product Number" in the newly created item in the "Product Number Request" list and assign to the value of "LastNumber"  in the “Counter” list.

Here is the outline of what I am looking for: https://splittingshares.wordpress.com/2008/04/11/auto-increment-a-number-in-a-new-list-item/

How do I set this up using SharePoint designer workflow?

Any help is appreciated.

techie