Simplify the following expression
$ \iint_{-\infty}^{c+x}xf(x)f(y) \,dy\,dx+\iint_{c+x}^{\infty}yf(x)f(y) \,dy\,dx $
where $x$ and $y$ are iid random variables; $c$ is a constant; and $f$ is the probability density function. You may call the CDF as $F(\cdot)$.