What is the single digit of the sum of the product of 2016 2017 multiplication and the product of 2017 2016 multiplication.
2016个2017连乘的积与2017个2016连乘的积相加的和的个位数字是多少．
<gadget id="calculator">1 + 6</gadget>
<output>7</output>

<result>7</result>