10394 - Twin Primes
This problem is a simple prime calculating problem. You have to find twin prim numbers. A pair of twin numbers e.g. is (3,5). Or in general (p, p+2)
The time limit allows you to precalculate all primes between 2 and 20000000. Then you can look for all twin primes in that intervall. After that it is easy to find the n-th twin primes.
1 2 3 4
(3, 5) (5, 7) (11, 13) (17, 19)