A straight horizontal rod is fixed in place. A small ring of mass $m$ is threaded on the rod, and the coefficient of static friction between the ring and the rod is $\mu_s$. A string is attached to the ring. A student pulls the string with a tension $T$ such that the string lies entirely in the horizontal plane and makes an angle $\theta$ with the rod. What is the minimum tension $T$ required to make the ring start sliding along the rod? (Assume $\cot\theta > \mu_s$).