Optimization needed (must run faster)

[masotrix]

Tested on http://codeforces.com/problemset/problem/802/N and
got TLE on test #6... input of just 500 from a maximum of 2200.

[masotrix]

PS: This apart from the needed adaptation to return unsigned long integers, for problems like the one posted... (I adapted it on my own, but you know, it is not related to the speed of the algorithm...)