Wang Bin wants to buy a copy of "Science and Technology Expo" for 12.70 yuan, and he can buy another copy by adding 3.90 yuan to his current money. But he only bought a copy of "Story Club" for 6.80 yuan. How much money does Wang Bin have left?
王彬想买一本12.70元的《科技博览》，他现在的钱再添3.90元，正好买一本．但他只买了一本6.80元的《故事会》，王彬还剩多少钱？
<gadget id="calculator">12.7 - 3.9 - 6.8</gadget>
<output>2</output>

<result>2</result>