A point electric dipole with dipole moment $p$ is placed in an external uniform electric field whose strength equals $E_0,$ with $\overrightarrow{p} \Vert {\overrightarrow{E}}_0.$ In this case, one of the equipotential surfaces enclosing the dipole form a sphere centered at dipole. If radius of the sphere in S.I. units is ${(x\times {10}^9\times \frac{p}{E_0})}^{\frac{1}{3}}$ , then $x$ is