Terminate loop in user decision step

Dear Experts,

                     I have a user decision step in my workflow; which has two buttons e.g; approve and reject buttons. this step is in the loop. I want to terminate the loop when user click on Approve button. How I should capture the ID of approve button. OR there is some other idea to terminate the loop; as I don't have any other condition to stop the loop.

Regards,

Sohail