Reverse the order of a four-digit number to get a new four-digit number. If the new number is 7992 greater than the original number, what is the largest original number among all four-digit numbers that meet this condition.
将一个四位数的数字顺序颠倒过来，得到一个新的四位数．如果新数比原数大7992，那么所有符合这样条件的四位数中原数最大的是多少．
<result>1_999</result>