A bag contains 5 red balls, 5 white balls, 5 blue balls and 5 yellow balls of the same size. Close your eyes and touch. If you want to touch the balls, there must be 2 balls of the same color. How many balls must you touch at least?
袋子里有同样大小的红球、白球、蓝球和黄球各5个．闭上眼睛摸，要想摸出的球一定有2个同色的，最少要摸出多少个球．
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>