Give an example of a finction $f(x)$ such that $f(x)>0$ $\forall x\in[a,b]$, where $\sqrt{f}$ is Riemann integrable but $f$ is not.

Question

Give an example of a finction $f(x)$ such that $f(x)>0$ $\forall x\in[a,b]$, where $\sqrt{f}$ is Riemann integrable but $f$ is not.

I don't know the example. Please help.