I have another Riemann integration related issue...

Let f:[a,b]-->R be bounded. Prove that f is Riemann integrable if and only if there exists a real number A such taht for any arbitrary epsilon >0 there exists d>0 such that |S(P,f) - A| < epsilon for every choice of S(P,f) associated with a partition P of [a,b], where |P|< d.

Im a bit confused as to how to find a d that satisfies |P| < d and how to associate that with the problem...