This is what I need to do but don't know where to start, please give me some pointers. It has to do with expected value of nonnegative random variable.

Let $\displaystyle X\in {0,1,2,...}$

Show that $\displaystyle E(X)=\sum_{k=0}^{\infty}1-F_X(k)$

I know that $\displaystyle E(X)=\sum_{k=0}^{\infty}xp(k)$,

but what is $\displaystyle p(k) $and$\displaystyle F_X(k)$?

Where do i even start?