1+2-3-4+5+6-7-8+9+10-11-12+...+1993+1994-1995-1996+1997+1998.
1+2-3-4+5+6-7-8+9+10-11-12+…+1993+1994-1995-1996+1997+1998．
<gadget id="calculator">1_990 - 1_991 - 1_992</gadget>
<output>-1_993</output>

<gadget id="calculator">(-1_993) + 1_993</gadget>
<output>0</output>

<gadget id="calculator">1_994 - 1_995 - 1_996</gadget>
<output>-1_997</output>

<gadget id="calculator">(-1_997) + 1_997</gadget>
<output>0</output>

<gadget id="calculator">1 + 0 + 0 + 1_998</gadget>
<output>1_999</output>

<result>1_999</result>