Using a balance and 1 weight each of 1 gram, 2 gram, 4 gram, and 8 gram (the weight can be placed on one side or both sides of the balance), what is the maximum number of different weights that can be weighed?
用一台天平和重1克、2克、4克、8克的砝码各1个(砝码可以放在天平一边或两边)，可称出不同的重量最多的种数是多少．
<gadget id="calculator">1 + 2 + 4 + 8</gadget>
<output>15</output>

<result>15</result>