For the cantilever beam of span $3$ m (shown below) m concentrated load of $20 \: kN$ applied at the free end causes a vertical displacement of $2$ mm at a section located at a distance of $1$ m from the fixed end. If a concentrated vertically downward load of $10$ kN is applied at the section located at a distance of $1$ m from the fixed end (with no other load on the beam), the maximum vertical displacement in the same beam (in mm) is ______