There is a series of numbers 1, 1989, 1988, 1987, ..., starting from the third number, each number is the difference between the number of the largest number and the number of the first two numbers, then what is the 1989th number.
有一列数1，1989，1988，1987，…，从第三个数起，每一个数都是它前面两个数中大数减小数的差，那么第1989个数是多少．
<gadget id="calculator">1_989 / 3</gadget>
<output>663</output>

<gadget id="calculator">663 - 1</gadget>
<output>662</output>

<gadget id="calculator">662 * 2</gadget>
<output>1_324</output>

<gadget id="calculator">1_989 - 1_324</gadget>
<output>665</output>

<result>665</result>