There is an array consisting of two numbers: (1, 3), (2, 5), (3, 7), (4, 9)..., what is the sum of the two numbers in the 1999th array.
有一列由两个数组成的数组：(1，3)、(2，5)、(3，7)、(4，9)…，第1999个数组中两个数的和是多少．
<gadget id="calculator">1_999 * 2</gadget>
<output>3_998</output>

<gadget id="calculator">3_998 + 1</gadget>
<output>3_999</output>

<gadget id="calculator">3_999 + 1_999</gadget>
<output>5_998</output>

<result>5_998</result>