An arithmetic sequence, the first term is 3, its last term is 2009, and the tolerance is 2, how many numbers are there in this series?
一个等差数列，首项是3，它的末项是2009，公差是2，这个数列一共有多少个数？
<gadget id="calculator">2_009 - 3</gadget>
<output>2_006</output>

<gadget id="calculator">2_006 / 2</gadget>
<output>1_003</output>

<gadget id="calculator">1_003 + 1</gadget>
<output>1_004</output>

<result>1_004</result>