Anyone else who cried after solving this? I tried to solve this for 2 hours. Time out. Always.

So, I tried to use dyanmic stack in CPP to store already found even numbers... Still the last one gave me timeout.

Solution ?

1) Add 2 and 3 to stack. 
2) If n <= Size of stack, get item at position n and output answer
3) Else, start from last element of stack, check if prime
4) To check for prime, recursively divide from each element in stack. If remainder 0 for any element in stack, not a prime. Break loop
5) If Prime, add to stack
6) Search only odd numbers

That's it. Now the last one which always timed out gave result in 0.3 seconds.