I have derived an expression which is giving correct results for the input given on the problem page as well as the ones below :

2
1000000 1 1
1000000000 1 1

500
15811

I got this set from another thread on this problem, however I am still getting WA on test 2. I am rounding off the result in Python :

round(abs(n))

and checking for the case when this will round to 0, which will happen for this case :

1 2 1

In which case I output 1.

What's special about test 2 ? Can I get a similar test or an idea about the special conditions which have to be checked ?