A pebble of irregular shape is completely submerged in a cylindrical fish tank. The water level in the fish tank rises by 1 cm. If the radius of the bottom of the fish tank is 20 cm, what is the volume of the pebble?
把一块形状不规则的鹅卵石完全浸入一个圆柱形的鱼缸里，鱼缸里的水面上升1cm，如果这个鱼缸的底面半径是20cm，那么这块鹅卵石的体积是多少？
<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">3.14 * 400 * 1</gadget>
<output>1_256</output>

<result>1_256</result>