A wedge of mass $m$ rests on a frictionless horizontal floor. Its base has fixed horizontal length $L$, and its inclined surface makes angle $\theta$ with the floor. A block of mass $2m$ is placed at rest at the top of the inclined surface and released. Every contact surface is frictionless, and the wedge is free to slide along the floor. For a fixed value of $L$, which value of $\theta$ minimizes the time for the block to reach the floor?