What is the sum of all the numbers in the natural numbers from 1 to 1001?
1到1001这些自然数中的所有数字之和是多少．
<gadget id="calculator">1 + 9</gadget>
<output>10</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">10 * (9/2) * 100 * 3</gadget>
<output>13_500</output>

<gadget id="calculator">1 + 1 + 1</gadget>
<output>3</output>

<gadget id="calculator">13_500 + 3</gadget>
<output>13_503</output>

<result>13_503</result>