There are three cubes of the same size, and the six faces of each cube are marked with six numbers from 1 to 6. When placed randomly, how many different numbers are there in the sum of the numbers on the three upward faces of the three cubes? value of .
有三个一样大小的立方体，每个立方体的六个面上都分别标有l～6这六个数字，那么当任意摆放时，三个立方体向上的三个面的数字之和有多少种不同的取值．
<gadget id="calculator">6 + 6 + 6</gadget>
<output>18</output>

<gadget id="calculator">1 + 1 + 1</gadget>
<output>3</output>

<gadget id="calculator">18 - 3</gadget>
<output>15</output>

<gadget id="calculator">15 + 1</gadget>
<output>16</output>

<result>16</result>