The surface tension ($\gamma$) of a solution, prepared by mixing 0.02 mol of an organic acid in 1 L of pure water, is represented as $$\gamma^* - \gamma = A \log(1 + Bc)$$ $\gamma^*$ is the surface tension of pure water, $A = 0.03 \text{ N m}^{-1}$, $B = 50 \text{ mol}^{-1} \text{ L}$ and $c$ is concentration in mol L $^{-1}$. The excess concentration of the organic acid at the surface of the liquid, determined by Gibbs adsorption equation at 300 K is $n \times 10^{-6} \text{ mol m}^{-2}$. The value of $n$ (rounded off to two decimal places) is $\underline{\hspace{2cm}}$. (Given: $R = 8.314 \text{ J K}^{-1} \text{ mol}^{-1}$)