Take n numbers from 1, 2, 3, ..., 2016 and multiply them. If the single digit of the product is 1, find the maximum value of n.
从1，2，3，…，2016中取出n个数相乘，若乘积的个位数字是1，求n的最大值．
<gadget id="calculator">201 * 2</gadget>
<output>402</output>

<gadget id="calculator">202 + 402 + 200</gadget>
<output>804</output>

<result>804</result>