GA Q8

For positive real numbers $S$ and $K$, the function $H_{K}(S)$ is defined as: $H_{K}(S)=\max (S-K, 0)$. The max function is defined as:

$$\max (a, b)=\left\{\begin{array}{ll} a, & \text { when } a>b \\ b, & \text { when } a \leq b \end{array}\right.$$

The graph below shows the plot of a function $N(S)$ versus $S$. $N(S)$ can be expressed as $\_\_\_\_$.