Conducting shells are awesome!

Two concentric conducting shells $A$ and $B$ have radii $a$ and $b,$ respectively $(b>a).$ Initially, the charges on the spheres are such that they have an equal electric potential $V.$

As a thought experiment, what would be the electric potential of $B$ , if we added just enough charge on $A$ $($ without disturbing the charge on $B)$ to make the electric potential of $A$ zero?