Among the natural numbers from 1 to 50, what is the difference between the sum of all even numbers and the sum of all odd numbers?
在1～50这些自然数中，所有偶数的和减去所有奇数的和，差等于多少．
<gadget id="calculator">2 + 50</gadget>
<output>52</output>

<gadget id="calculator">25 / 2</gadget>
<output>25/2 = around 12.5</output>

<gadget id="calculator">52 * (25/2)</gadget>
<output>650</output>

<gadget id="calculator">1 + 49</gadget>
<output>50</output>

<gadget id="calculator">50 * (25/2)</gadget>
<output>625</output>

<gadget id="calculator">650 - 625</gadget>
<output>25</output>

<result>25</result>