There is a formula 6*5*4*3*2*1. Xiao Ming replaced some "*" with "/" in the above formula, and the calculation result is still a natural number, so what is the smallest natural number?
有一个算式6*5*4*3*2*1．小明在上式中把一些"*"换成"/"，计算结果还是自然数，那么这个自然数最小是多少？
<gadget id="calculator">4 / 3 / 2</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">6 * 5 * (2/3) * 1</gadget>
<output>20</output>

<result>20</result>