A capacitor of capacitance $\mathrm{C}$ and potential $\mathrm{V}$ has energy $\mathrm{E}$. It is connected to another capacitor of capacitance $2 \mathrm{C}$ and potential $2 \mathrm{~V}$. Then the loss of energy is $\frac{x}{3} \mathrm{E}$, where $x$ is _______.