calculus - Example of a continuous function which is not smooth

I need a function which is continuous but not smooth ( not a $C^{\infty})$.

Smooth functions are those whose derivatives of all order exists. For example $f(x)= e^{x}$ is a smooth function while $f(x)=|x|$ is not smooth as derivative at $0$ does not exist.

But what I require is functions in from $\mathbb{R}^{n} $ to $\mathbb{R}^{m}$.

For simplicity it is enough to give functions from $\mathbb{R}^{2} $ to $\mathbb{R}^{2}$. I have examples of discontinuous functions from $\mathbb{R}^{2} $ to $\mathbb{R}^{2}$ , like $\frac{xy}{x^{2}+y^{2}}$ which is not continuous at $(0,0)$.