Upper bound on expectation given probability [closed]

Let $X$ be a positive random variable. I know that $\mathbb{P}[X \leq a] \geq q$. Any hints about how to find an upper bound on $E[X]$ in terms of $q$ and $a$?Using Markov inequality, I can obtain $E[X] \geq a(1-q)$. But I need an upper bound, not a lower one. Any hints? Thanks!