There are about 9,000 species of birds on the earth, reptiles belong to birds (2/3), non-mammals belong to reptiles (1/3), how many kinds of non-mammals are there?
地球上鸟类约有9000种，爬行动物是鸟类的(2/3)，非哺乳动物又是爬行动物的(1/3)，非哺乳动物约有多少种？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">9_000 * (2/3)</gadget>
<output>6_000</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">6_000 * (1/3)</gadget>
<output>2_000</output>

<result>2_000</result>