The natural numbers a, b, c, and d are not equal to each other. It is known that a•b•c•d=2013, then how much is a+b+c+d=.
自然数a，b，c，d互不相等，已知a•b•c•d=2013，那么a+b+c+d=多少．
<gadget id="calculator">1 + 3 + 11 + 61</gadget>
<output>76</output>

<result>76</result>