In the story "The Crow Drinks Water", there is a cuboid glass with a length of 5cm, a width of 10cm, and a height of 50cm, but the water is only 2dm high. If a crow wants to drink water, it must raise the water level to 45cm. The volume of stones is 2cm**2. How many small stones does the crow have to throw into the water to drink water?
《乌鸦喝水》的故事中，有一个长5cm，宽10cm，高50cm的长方体玻璃杯，但水只有2dm高，乌鸦要想喝水，必须使水面升高到45cm，现有若干块正方体小石头，体积均为2cm**2，乌鸦要往水中扔多少块小石头才能喝到水？
<gadget id="calculator">2 * 10</gadget>
<output>20</output>

<gadget id="calculator">45 - 20</gadget>
<output>25</output>

<gadget id="calculator">25 / 2</gadget>
<output>25/2 = around 12.5</output>

<gadget id="calculator">5 * 10 * (25/2)</gadget>
<output>625</output>

<result>625</result>