In Horton's equation fitted to the infiltration data for a soil, the initial infiltration capacity is $10 \mathrm{~mm} / \mathrm{h}$; final infiltration capacity is $5 \mathrm{~mm} / \mathrm{h}$; and the exponential decay constant is $0.5 / \mathrm{h}$. Assuming that the infiltration takes place at capacity rates, the total infiltration depth (in $\mathrm{mm}$ ) from a uniform storm of duration $12 \mathrm{~h}$ is___________. (round off to one decimal place)