There are 1 gram, 2 gram, 4 gram, and 8 gram weights, how many different weights can be weighed?
现有1克、2克、4克、8克、的砝码各1个，能称出多少种不同的重量．
<gadget id="calculator">1 + 2 + 4 + 8</gadget>
<output>15</output>

<result>15</result>