A stone must fly over two walls of height $h_1$ and $h_2$ $(h_2~ > ~h_1)$ from the side of the lower wall. The distance between the upper points of the two walls near which the stone's trajectory lies is $L$. Find the minimum velocity of the stone. (source: AN Matveev's Mechanics and Relativity).

Answer:$\sqrt{g(h_1+h_2+L)}$, where $g$ is acceleration due to gravity

The rather terse nature of the problem statement is very typical of Russian texts. I'm an intermediate/advanced self-learner and I love to wrangle with these kinds of problems. This problem seemed like a basic projectile motion problem but this has got me in knots - If the limiting height is $h_2$, why does the problem need $h_1$? And, there is no angle to use either. What's the significance of the requirement for minimum velocity? Clearly, it has to cross the walls, and based on what I see, $h_1$ likely lies below the trajectory and $h_2$ must just touch the trajectory and this can potentially give the velocity. But, I'm unable to find the approach to solve this. Can anyone provide a way to think about this problem?