Figure  shows  a light  rod of length  L rigly attached   to a small  heavy block  at one end  a hook  at other  end. The rod is in horizontal position . There is a fixed  smooth  ring  at a depth h below  the  initial position  of the hook  and the  hook  gets into  the rings  as it reaches  there. The minimum  value  of the  h so that the block  moves in  a complete  circle about  the ring  is $L^X$.x is