Calculation: 1+2+3+4+...+399+400=how much.
计算：1+2+3+4+…+399+400=多少．
<gadget id="calculator">1 + 400</gadget>
<output>401</output>

<gadget id="calculator">400 / 2</gadget>
<output>200</output>

<gadget id="calculator">401 * 200</gadget>
<output>80_200</output>

<result>80_200</result>