DIY on a ladder

A uniform ladder with mass m₂ and length L rests against a smooth wall. A do-it-yourself enthusiast of mass m₁ stands on the ladder a distance d from the bottom (measured along the ladder). The ladder makes an angle θ with the ground. There is no friction between the wall and the ladder, but there is a frictional force of magnitude f  between the floor and the ladder. N₁ is the magnitude of the normal force exerted by the wall on the ladder, and N₂ is the magnitude of the normal force exerted by the ground on the ladder. Throughout the problem, consider counterclockwise torques to be positive. 

What is the minimum coefficient of static friction μ_min required between the ladder and the ground so that the ladder does not slip?