Calculation: (1+3+5+...+1989)-(2+4+6+...+1988)=how much.
计算：(1+3+5+…+1989)-(2+4+6+…+1988)=多少．
<gadget id="calculator">995 * 995</gadget>
<output>990_025</output>

<gadget id="calculator">995 * 994</gadget>
<output>989_030</output>

<gadget id="calculator">990_025 - 989_030</gadget>
<output>995</output>

<result>995</result>