A block of mass $m$ is on a frictionless horizontal table between two parallel vertical walls, initially separated by a distance $L_0$. The block is connected to the left wall by a massless spring of spring constant $k$, and to the right wall by another massless spring of spring constant $k$. The block oscillates along the line between the walls with amplitude $A_0$. At a certain moment, the right wall begins to move toward the left wall at a constant, very small speed $v$ (where $v \ll A_0\sqrt{k/m}$). After the right wall has moved a total distance $d$ (with $A_0 \ll d \ll L_0$), it stops. Assume the springs remain within their linear limits at all times. What is the new amplitude of the block's oscillation?