A piece of briquette is 9cm high and 12cm in diameter. There are 12 small holes on it, each with a diameter of 2cm. How many cubic decimeters of coal should a piece of briquette have?
一块蜂窝煤，高9cm，直径12cm，上面有12个小孔，每个直径为2cm，一块蜂窝煤至少要煤多少立方分米．
<result>0.67824</result>