[firedrake] Fw: Runing problem

Dear all, I'm beginner in Firedrake so I preferred to start with examples which there are in the website. I copied the code of Helmholtz example and saw the contour plot of error but the amount of error wasn't printed. After any run, I should stop the running with ctrl+z. The python file of code and the screenshot of my desktop have been attached. Many thanks if someone guide me about this problem. Best, Amireh