After heaving goggling, I found a link in which approach of solving sum of floor functions is given. Due to lack of time I was unable to code it.
Had anyone solved with this approach and getting all test cases partially or fully passed?
Euler Sum Probable approach
swamicoder
#1
avi224
#3
I used the approach.

50 points: I stored 200 digits of e and used this to get the answer.

100 points: I used this algorithm(link) to get the first 8000 digits of e.