A Pythagorean triplet is a set of three natural numbers, a b c, for which,
a^2 + b^2 = c^2
3^2 + 4^2 = 9 + 16 = 5^2 = 25.
There exists exactly one Pythagorean triplet for which a + b + c = N (the input).
Find the product abc.
Thank you to Project Euler Problem 9.