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I want to say that I'm impressed by this task! This problem really tests how fast your hands (and your browser) are.
Had heart beating like I tried to run for 100 meters in 10 seconds :).
Well :) I looked into the checker code - it really has 70 seconds limit... I hope your browser opens pages faster than that... As a matter of fact if you would like, you can automate browser or probably submit solutions from console (or your IDE) supplying sessionid to them :)
I understand it is not very comfortable - sites which compile and run solutions on server have easier way to impose time limit. So that is our "price" for checking tasks by answer only...