To derive the total flood hydrograph at a catchment outlet from an isolated storm, the order in which the following methods are applied, from the first method to the last method, is

P. Obtaining the hyetograph

Q. Addition of baseflow

R. Estimation of initial and infiltration losses

S. Application of unit hydrograph

The ordinates of a one-hour unit hydrograph for a catchment are given below: 

$$ \begin{array}{|l|l|l|l|l|l|l|l|l|} \hline t(\text { hour }) & 0 & 1 & 2 & 3 & 4 & 5 & 6 & 7 \\ \hline Q\left(\mathrm{~m}^3 / \mathrm{s}\right) & 0 & 9 & 21 & 18 & 12 & 5 & 2 & 0 \\ \hline \end{array} $$

Using the principle of superposition, a D-hour unit hydrograph for the catchment was derived from this one-hour unit hydrograph. The ordinates of the D-hour unit hydrograph were obtained as 3 m3/s at t = 1 hour and 10 m3/s at t = 2 hour. The value of D (in integer) is _____________.