Use 10 numbers from 0 to 9 to form 3 three-digit numbers and 1 single-digit number so that their sum is 999. To make the largest three-digit number as large as possible, what is the largest three-digit number?
用0～9这10个数字组成3个三位数和1个一位数，使它们的和是999，要使得最大的三位数尽可能大，则这个最大的三位数是多少．
<result>649</result>