Seven consecutive natural numbers, the sum of the largest two numbers is greater than the smallest number by 1997, what is the middle number?
七个连续的自然数，最大的两个数的和比最小的数大1997，那么中间的那个数是多少．
<gadget id="calculator">1_997 - 2 - 3 - 3</gadget>
<output>1_989</output>

<gadget id="calculator">1 - 1</gadget>
<output>0</output>

<gadget id="calculator">1 + 0</gadget>
<output>1</output>

<gadget id="calculator">1_989 / 1</gadget>
<output>1_989</output>

<result>1_989</result>