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I have a Cyber cafe so I need to run the PC all day so whether mining or not PC is on only. SO for just mining the electricity cost is virtually nil.

Check out Gridcoin. You won't get rich but you can make money with CPUs - it also can be set to only run when computer isn't in use so probably good for a cyber cafe. Your clients won't notice any slowdown and you make some money when computer is not in use. It also contributes to science/math research so you get to do some good too.