Among the 2005 natural numbers from 1 to 2005, what is the difference between the sum of all odd numbers and the sum of even numbers?
1到2005这2005个自然数中，所有奇数之和与偶数之和的差是多少．
<gadget id="calculator">2_004 - 2_003</gadget>
<output>1</output>

<gadget id="calculator">1 * 1_002</gadget>
<output>1_002</output>

<gadget id="calculator">2_005 - 1_002</gadget>
<output>1_003</output>

<result>1_003</result>