I guess I can use LLN...

Show that for any sequence $\displaystyle X_1,\dots,X_n,\dots$ of iid random variables, $\displaystyle \frac{1}{n^2}\sum_{i=1}^n iX_i\to \frac{m}{2} \;\;a.s.$ if and only if $\displaystyle X_1$ is integrable and $\displaystyle \mathbb{E}[X_1]=m$.

Thanks.