Vikas has a rectangular farm of dimensions $a*b$ in 'Amazon' forest. He also has $4$ cows. The $4$ cows are very aggressive. So he ties his cows to the $4$ corners of the farm through ropes. The length of ropes are $r1, r2, r3, r4$. He wants to maximise the grazing area. But, as the cows are aggressive, he does not want the cows to fight.

$F(a, b) =$ Maximum area of the farm that can be grazed by the cows

$S(a, x) = \sum_{b=a}^x F(a, b)$

Output $\lfloor S(4, 1000) \rfloor$