A spring is hung vertically from a fixed support. When an object of mass m is attached to the end of the spring, it stretches by a distance y. When an object of mass of 2m is hung from the spring, it stretches by a distance 2y. The same spring is then set up in a pulley system as shown in the drawing. Here an object of mass m is suspended from a light rope that passes over each pulley and connects to the two ends of the spring. By what distance is the spring stretched in this configuration? Express your answer in terms of the original stretch distance y.