A rigid block of mass $m_1=10$ kg having velocity $v_0=2 \: m/s$ strikes a stationary block of mass $m_2=30$ kg after traveling $1$ m along a frictionless horizontal surface shown in the figure.

The two masses stick together and jointly move by a distance of $0.25$ m further along the same frictionless surface, before they touch the mass-less buffer that is connected to the rigid vertical wall by means of a linear spring having a spring constant $k=10^5 \: N/m$. The maximum deflection of the spring is _________ cm (round off to $2$ decimal places)