Goldbach's conjecture states that any even number greater than 2 can be written as the sum of two prime numbers. For example:

4 =	2 +	2
6 =	3 +	3
8 =	3 +	5
...

Instead, Ada Byron's setters propose Goddbach's conjecture: "any odd number greater than 1, which is not prime, can be described as the sum of two prime numbers. ". The first odd numbers greater than 1, which are not prime are: 9, 15, 21, ... and:

9 =	2 +	7
15 =	2 +	13
21 =	2 +	19
...

Unfortunately, Goddbach conjecture does not hold, and 27 is the first odd number that, not being prime, cannot be expressed as the sum of two prime numbers. But what can be done is to elaborate the Goddbach sequence, $$$\mathcal{G}$$$, with all the odd numbers that are not prime and can be written as the sum of two prime numbers. In this series, $$$\mathcal{G}_1=9$$$, $$$\mathcal{G}_2=15$$$, $$$\mathcal{G}_3=21$$$, ...

Given an index $$$i$$$, you are asked to compute the number at that position in $$$\mathcal{G}$$$, the Goddbach sequence, $$$\mathcal{G}_i$$$.

3
1
3
103

9
21
759