## Maximal Area

### Problem 681

Given positive integers $a \le b \le c \le d$, it may be possible to form quadrilaterals with edge lengths $a,b,c,d$ (in any order). When this is the case, let $M(a,b,c,d)$ denote the maximal area of such a quadrilateral.

For example, $M(2,2,3,3)=6$, attained e.g. by a $2\times 3$ rectangle.

Let $SP(n)$ be the sum of $a+b+c+d$ over all choices $a \le b \le c \le d$ for which $M(a,b,c,d)$ is a positive integer not exceeding $n$.

$SP(10)=186$ and $SP(100)=23238$.

Find $SP(1\,000\,000)$.