The greatest four digit perfect square number is = ?

$$\eqalign{ & \,\,\,\,\,\,\,9|\overline {99} \,\,\overline {99} \,\,(99 \cr & \,\,\,\,\,\,\,\,\,\,|\,81 \cr & \,\,\,\,\,\,\,\,\,\,| - - - - - - \cr & \,189|\,18\,99 \cr & \,\,\,\,\,\,\,\,\,\,|\,17\,01 \cr & \,\,\,\,\,\,\,\,\,\,| - - - - - - \cr & \,\,\,\,\,\,\,\,\,\,|\,\,\,\,1\,98 \cr & \therefore {\text{Required number}} \cr & = \left( {9999 - 198} \right) \cr & = 9801 \cr} $$