Two identical concave mirrors are set facing each other 1.0 m apart.A small lightbulb is placed halfway between the mirrors.A small piece of paper placed just to the left of the bulb prevents light from the bulb from directly shining on the left mirror, but light reflected from the right mirror still reaches the left mirror. A good image of the bulb appears on the left side of the piece of paper. What is the focal length of the mirrors?