100-99+98-97+...+2-1+2-3+4-...-99+100=how many.
100-99+98-97+…+2-1+2-3+4-…-99+100=多少．
<gadget id="calculator">100 - 99</gadget>
<output>1</output>

<gadget id="calculator">1 * 50</gadget>
<output>50</output>

<gadget id="calculator">50 + 1 + 50</gadget>
<output>101</output>

<result>101</result>