There are some (at least $3$) elves in Santa's backyard. The backyard has a circular shape with diameter $d$. Santa finds that any three elves can be surrounded by an $\ell \times d$ rectangle. Prove that all the elves can be surrounded by a $2\ell \times d$ rectangle. Note: An elf being "surrounded" by a rectangle means that the point corresponding to the elf is contained within the rectangle, or is on its perimeter. The elves have no areas, they are points.