Which is the correct formula for the economic order quantity?

$($Q$/2)$H

$($D$/$Q$)$H

$(\frac{Q}{2})H+(\frac{D}{Q})S$

$\sqrt[\phantom{2}]{\frac{2DS}{H}}$

Q$/$D

$\frac{D}{Q}$

$($D$/$Q$)$S