Find Lighted Area

You are given a square with side length $2L$. The coordinates of its vertices are at $(-L, -L)$, $(L, -L)$, $(L, L)$, and $(-L, L)$. You are also given $N$ disks (each disk is opaque, and light rays cannot pass through them) each of radius $R$. The centers of each of the disks are at a fixed distance $D$ from the origin $(0, 0)$. This distance $D$ is strictly greater than $R$. It is guaranteed tha