1+2-3-4+5+6-7-8+9+10-11-12...+1989+1990-1991-1992+1993+1994=how much.
1+2-3-4+5+6-7-8+9+10-11-12…+1989+1990-1991-1992+1993+1994=多少．
<gadget id="calculator">1 + 1_993</gadget>
<output>1_994</output>

<gadget id="calculator">499 / 2</gadget>
<output>499/2 = around 249.5</output>

<gadget id="calculator">1_994 * (499/2)</gadget>
<output>497_503</output>

<gadget id="calculator">2 + 1_994</gadget>
<output>1_996</output>

<gadget id="calculator">1_996 * (499/2)</gadget>
<output>498_002</output>

<gadget id="calculator">3 + 1_991</gadget>
<output>1_994</output>

<gadget id="calculator">498 / 2</gadget>
<output>249</output>

<gadget id="calculator">1_994 * 249</gadget>
<output>496_506</output>

<gadget id="calculator">4 + 1_992</gadget>
<output>1_996</output>

<gadget id="calculator">1_996 * 249</gadget>
<output>497_004</output>

<gadget id="calculator">498_002 - 496_506 - 497_004</gadget>
<output>-495_508</output>

<gadget id="calculator">497_503 + (-495_508)</gadget>
<output>1_995</output>

<result>1_995</result>