A parallel plate capacitor is of area $6 \mathrm{~cm}^2$ and a separation 3 mm . The gap is filled with three dielectric materials of equal thickness (see figure) with dielectric constants $\mathrm{K}_1=10, \mathrm{~K}_2=12$ and $\mathrm{K}_3=14$. The dielectric constant of a material which when fully inserted in above capacitor, gives same capacitance would be