In this problem 557B - Pasha and Tea : I got a wrong answer with this submission 11854334 But I run the same program in my pc it can return the correct answer '1000000000'.

So I left a comment and asked for help, a nice guy 'brighterstill' helped and updated my code and get accepted : 11869049

So I now have two questions, why my code is wrong and why changed to double make it right ....

Please help, thanks