Cauchy-Riemann equations

Let $u(x,y)$ and $v(x,y)$ be continuous functions that satisfy the following equations:

$u_x = v_y \\ u_y = -v_x$

Suppose the first and second partial derivatives of $u$ and $v$ are continuous in both $x$ and $y$ .

Find $u_{xx}+u_{yy}$ .