A thin soap bubble of radius $R=1$ cm, and thickness $a=3.3 \mu m (a << R)$, is at a potential of $1$ V with respect to a reference point at infinity. The bubble bursts and becomes a single spherical drop of a soap (assuming all the soap is contained in the drop) of radius $r$. The volume of the soap in the thin bubble is $4 \pi R^{2} a$ and that of the drop is $\frac{4}{3}\pi r^{3}$. The potential in volts, of the resulting single spherical drop with respect to the same reference point at infinity is _________. (Give the answer up to two decimal places.)