HMMT 2021 G7

Let $O$ and $A$ be two points in the plane with $O A=30$, and let $\Gamma$ be a circle with center $O$ and radius $r$. Suppose that there exist two points $B$ and $C$ on $\Gamma$ with $\angle A B C=90^{\circ}$ and $A B=B C$. Compute the minimum possible value of $\lfloor r\rfloor$.