Among the three-digit numbers composed of numbers 1, 7, and 8 without repeating numbers, what is the largest three-digit number minus the smallest three-digit number?
用数字1、7、8组成的没有重复数字的三位数中，最大的三位数减最小的三位数等于多少
<gadget id="calculator">871 - 178</gadget>
<output>693</output>

<result>693</result>