Euler Sum (ES)

I tried solving Euler Sum in June Long contest but was not able to. I had no clue how to start. Can someone give me some idea on how to approach the same.

UPDATE:

If someone is still looking for solution to ES, here’s a link to an editorial(unofficial) on codechef discuss.

Can anyone come up with a C++ solution for this problem??

The question seems to be a simple one like calculating the sum of a series but the trick in the question is to calculate the required sum with PRECISION to obtain the required answer.
I didn’t complete that question but know the approach of it, as follows:
There were two subtasks of 50 points each:
1st: n<=(10^100), i.e. Googol number(very large)
but for that all u need is to just calculate the value of e^235(for worst case) that provides u the actual value with precision of e^x upto 101-102 decimal places and we can then easily calculate last term that is n*(e^n) and also the lower terms like (n-1)*(e^(n-1)). So, focus on calculating the value of e^235 with the given constraints of 1000 B size and that too fast (1 sec). U can opt for FFT (Fast Fourier Transform) to do so, so please refer it.

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