To celebrate Children's Day, the grandfather bought 8 copies of "Fun Mathematics" and distributed them to the three granddaughters Xiaolan, Xiaohua and Xiaomei, so that each granddaughter has at least one book. How many ways are there in total?
为庆祝"六一"儿童节，爷爷买来8本《趣味数学》分给小兰、小花、小美三个孙女，使每个孙女至少有一本书，一共有多少种分法．
<gadget id="calculator">8 - 3</gadget>
<output>5</output>

<gadget id="calculator">6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>21</output>

<result>21</result>