A cube tank with a side length of 2 decimeters. Pour 5 liters of water into the tank, and then put a pebble into the water. At this time, the depth of the water is 15 cm. What is the volume of the pebble in cubic decimeters?
一个正方体水槽，棱长2分米，向水槽中倒入5升水后，再把一个鹅卵石放入水中，这时量得水深15厘米，鹅卵石的体积是多少立方分米？
<gadget id="calculator">5 / 2 / 2</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">1.5 - (5/4)</gadget>
<output>0.25</output>

<gadget id="calculator">2 * 2 * 0.25</gadget>
<output>1</output>

<result>1</result>