In an electrochemical reaction of lead, at standard temperature, if $\mathrm{E}^{0}\left(\mathrm{~Pb}^{2+} / \mathrm{Pb}\right)=\mathrm{m}$ Volt and $\mathrm{E}^{0}\left(\mathrm{~Pb}^{4+} / \mathrm{Pb}\right)=\mathrm{n}$ Volt, then the value of $\mathrm{E}^{0}\left(\mathrm{~Pb}^{2+} / \mathrm{Pb}^{4+}\right)$ is given by $\mathrm{m-x n}$. The value of $\mathrm{x}$ is ___________. (Nearest integer)