1997+1996-1995-1994+1993+1992-1991-1990+...+9+8-7-6+5+4-3-2+1=how much.
1997+1996-1995-1994+1993+1992-1991-1990+…+9+8-7-6+5+4-3-2+1=多少．
<gadget id="calculator">4 - 3 - 2</gadget>
<output>-1</output>

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

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

<result>1_997</result>