A parallel plate capacitor with plate area $\mathrm{A}$ and separation between the plates $\mathrm{d}$ is filled with different dielectrics as shown in the figure. If the equivalent capacitance between $\mathrm{a}\mathrm{ }\&\mathrm{ }\mathrm{b}$ is $\frac{m\mathrm{A}{\epsilon }_0}{n\mathrm{d}}$ then find the value of $\left(m+n\right)$, where $m$ and $n$ are least positive integers.