When I checked the above product in my PC,it gave me a correct result,but when I submit the original problem(this multiplication is a sub problem of that,I am thinking of this possible product may occur in test cases) it says wrong answer(I am sure that rest of the part is perfectly fine).Is there a chance of over flow ?,I have used (long long int) data type.
I know this is not the place to ask this question, but i’m stuck on it and is looking over the net for a long time and haven’t got anything clear cut… if they are available they are not explained well…
so the question is
what are the methods to increase the speed of i/o operation like getchar unlocked fread unlocked i just know there name don’t know how to use them.
any kind of guidance will be very much help full 
links to resources(tutorials) will do the work.
grv.
NO. There will be no overflow in this calculation if you use long long. Error will be in some other step.
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