Calculate 1-(1+2)+(1+2+3)-(1+2+3+4)+…-(1+2+…+98)+(1+2+…+99)= how much ．
计算1-(1+2)+(1+2+3)-(1+2+3+4)+…-(1+2+…+98)+(1+2+…+99)=多少．
<gadget id="calculator">1 + 49</gadget>
<output>50</output>

<result>50</result>