Calculation: 1989+1988+1987-1986-1985-1984+...+9+8+7-6-5-4+3+2+1=how much
计算：1989+1988+1987-1986-1985-1984+…+9+8+7-6-5-4+3+2+1=多少
<gadget id="calculator">331 * 9</gadget>
<output>2_979</output>

<gadget id="calculator">2_979 + 6</gadget>
<output>2_985</output>

<result>2_985</result>