There are 15 red, green and blue chess pieces each, and you take them out of the box with your eyes closed, and you can only take one chess piece at a time. How many times do you take at least to ensure that there are 3 pieces of the same color.
有红、绿、蓝棋子各15个，你闭着眼睛从盒中往外拿，每次只能拿一个棋子．你至少拿多少次才能保证其中有3个棋子同一颜色．
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>