There are 6 yellow and 6 white ping pong balls of the same size in the box, at least how many balls must be touched to ensure that 2 ping pong balls of the same color can be touched.
盒子里有同样大小的黄色和白色乒乓球各6个，至少要摸多少个球，才能保证摸到两个同样颜色的乒乓球．
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>