Consider a complex reaction taking place in three steps with rate constants $\mathrm{k}_{1}, \mathrm{k}_{2}$ and $\mathrm{k}_{3}$ respectively. The overall rate constant $k$ is given by the expression $k=\sqrt{\frac{k_{1} k_{3}}{k_{2}}}$. If the activation energies of the three steps are 60,30 and $10 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively, then the overall energy of activation in $\mathrm{kJmol}^{-1}$ is $\_\_\_\_$ . (Nearest integer)