Four good friends A, B, C, and D stand in a line to take pictures. How many different ways do they stand?
甲、乙、丙、丁4个好朋友排成一队拍照，他们一共有多少种不同的站法．
<gadget id="calculator">4 * 3 * 2 * 1</gadget>
<output>24</output>

<result>24</result>