It is known that the real numbers a, b, c, and d are four unequal natural numbers, satisfying: (1/20)=(1/(a))+(1/(b))+(1/(c)) +(1/(d)), find the minimum value of a+b+c+d.
已知实数a、b、c、d是四个互不相等的自然数，满足：(1/20)=(1/(a))+(1/(b))+(1/(c))+(1/(d))，求a+b+c+d的最小值．
<gadget id="calculator">240 + 120 + 60 + 48</gadget>
<output>468</output>

<result>468</result>