equal to $5$. The edge $4$ becomes active and its label is set to $19-5=14$. The edge $(1,4)$ becomes used, and the vertex $1$ turns into inactive since there are no active edges originating from it. Hence, after two seconds the graph turns into the one shown in Figure \[fi:figure 2\].

![\[fi:figure 2\] The configuration after the second 2.](graph02.png)

The same procedure is repeated until the end of the $5$th second. In the $6$th second the edge $(1,5)$ gets its time parameter decreased to $0$ and the vertex $5$ gets activated. Its label becomes $19-2=17$. However, the edges $(4,5)$, $(5,9)$, and $(5,6)$ were already active and the water was flowing through them towards the vertex $5$.

The old flow of water through the edge $(4,5)$ will complete in additional $5$ seconds. However, when it completes the quality of the water that will reach the vertex $5$ will be $14-2=12$ which is lower than the label of the vertex $5$. Thus there is no point in keeping track of this water flow. On the other hand, the water flow that starts from $5$ and goes towards $4$ will have quality $17-2=15$ which is higher than the label of the vertex $4$. 