There are red, yellow, blue, white, and black balls of the same shape and size, and each person must choose 3 balls from them. To make two people get the ball with exactly the same color, at least how many people should participate in the ball selection.
有红、黄、蓝、白、黑五种形状大小完全一样的小球若干，每人必须从中选3只小球．要使有两人得到球的颜色完全一样，至少有多少人参加选球．
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>