The reading of the water meter in a factory is 71111 cubic meters. When four of the five-digit readings displayed by the water meter are the same, how many cubic meters of water did the factory use at least?
一家工厂的水表显示的读数是71111立方米，当水表显示的读数的五位数中有四个数字相同时，工厂至少又用了多少立方米水．
<gadget id="calculator">71_777 - 71_111</gadget>
<output>666</output>

<result>666</result>