No, I didn't. Because your question was "silly".
And if your binary search is "fine" then you would not be getting a WA.
There is only one thing that you have to do in this question, and that is binary search. So, if you have properly read wikipedia , for approximation of n! , and it seems you have, then if you are getting a WA, what could possibly be going wrong? Yes, that's right your "binary search". And i don't think that i can help you with that!
If you want big test cases "ask" for it.
I/P :
1
1000000
O/P:
2718274
PS: i didn't liked your "Hah" .