Given an even number (greater than 2), return two prime numbers whose sum will be equal to the given number.

A solution will always exist. See Goldbach’s conjecture [https://en.wikipedia.org/wiki/Goldbach%27s_conjecture].

Example:

Input: 4 Output: 2 + 2 = 4

If there are more than one solution possible, return the lexicographically smaller solution.

If [a, b] is one solution with a <= b, and [c, d] is another solution with c <= d, then

[a, b] < [c, d]

If a < c OR a==c AND b < d.