If none of your browsers let you run java applets anymore, you can just download the jar:
http://acm.timus.ru/Supplement/CalcEngine/CalcEngineGUI.jar

Then run it as:
java -cp CalcEngineGUI.jar CalcEngineApplet

Since you're able to download it, you can actually decompile it and submit the code to get accepted. There's a Thread.Sleep(3000) in there that you'll need to comment out.