There are 15 balls of red, yellow, blue, white, and black, and they are mixed in a ball box. If you are blindfolded, you will be caught. When touching balls in the ball box, at least how many balls must be drawn to ensure that there must be 2 balls of the same color.
有红、黄、蓝、白、黑五种球各15只，混放在一只球箱里，如果蒙住你的眼睛，让你在．球箱里摸球，至少要摸出多少个球才能保证必有2只球的颜色相同．
<gadget id="calculator">1 * 5</gadget>
<output>5</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<result>6</result>