There are 2 grams, 5 grams, and 20 grams each. How many different masses can be weighed using only the weights and a balanced balance?
有2克，5克，20克的砝码各一个，只用砝码和一架已经调节平衡了的天平，能称出多少种不同的质量．
<gadget id="calculator">3 + 3 + 1</gadget>
<output>7</output>

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

<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<gadget id="calculator">7 + 6</gadget>
<output>13</output>

<result>13</result>