Should the startup idea by an original one?

Actually I would argue that if you go into a market that has no competition it is a sign that there might not be a market there. However, that does not mean you do not need some magic sauce to differentiate yourself. It is the unique magic sauce in your idea that is required!

its not only about the idea , its about how you will introduce to your customer and what is new or different in your startup.

If you are confident that the execution of your idea will attract new users, and also encourage users of the other application to cross over then it's definitely worth going for it.

I always find with projects it's a mix of the idea and it's execution (by execution I mean a combination of development, usability and strategy of user acquisition). An idea on it's own provides little value if it is not executed (or executed well).