Add the same number to the numerator and denominator of the fraction (1997/1999), so that the new fraction is reduced to (1999/2000), then what is the added number?
分数(1997/1999)的分子、分母加上同样一个数，使新分数约分后为(1999/2000)，那么所加上的这个数是多少．
<gadget id="calculator">1_999 / 2_000</gadget>
<output>1_999/2_000 = around 0.9995</output>

<gadget id="calculator">(1_999/2_000) * 1_999</gadget>
<output>3_996_001/2_000 = around 1_998.0005</output>

<gadget id="calculator">(3_996_001/2_000) - 1_997</gadget>
<output>2_001/2_000 = around 1.0005</output>

<gadget id="calculator">1 - (1_999/2_000)</gadget>
<output>1/2_000 = around 0.0005</output>

<gadget id="calculator">(2_001/2_000) / (1/2_000)</gadget>
<output>2_001</output>

<result>2_001</result>