From the 2003 natural numbers 1, 2, 3, ..., 2002, 3003, take several natural numbers so that the sum of any two natural numbers cannot be divisible by 7. What is the maximum number that can be taken?
从1、2、3、…、2002、3003这2003个自然数中，取出若干个自然数，使其中任意两个自然数的和都不能被7整除，最多可以取多少个数．
<gadget id="calculator">286 * 2</gadget>
<output>572</output>

<gadget id="calculator">287 + 572 + 1</gadget>
<output>860</output>

<result>860</result>