Sequence 1, 1991, 1990, 1, 1989, 1988, 1, ... Starting from the third number, each number is the difference between the previous two numbers. In this sequence, how many items does the first zero appear in?
数列1，1991，1990，1，1989，1988，1，…从第三个数起，每个数是前两个数的差，这个数列中第一个零出现在第多少项．
<gadget id="calculator">1_992 / 2</gadget>
<output>996</output>

<gadget id="calculator">1_992 + 996</gadget>
<output>2_988</output>

<result>2_988</result>