Two blocks, of masses $1.0\ \text{kg}$ and $3.0\ \text{kg}$, lie on a smooth floor, joined by a light spring. The $1.0\ \text{kg}$ block touches a fixed wall. The $3.0\ \text{kg}$ block is pushed towards the wall, squeezing the spring by $0.20\ \text{m}$, and then released from rest, as shown in the figure. What is the largest stretch of the spring in the motion that follows?

Fig. 1: On a smooth floor, a block of mass 1.0 kg is pressed against a wall on the left and a block of mass 3.0 kg is on its right. A spring between the two blocks is squeezed by 0.20 m.