For four digits: \overline{abcd}, if there is a prime number P and a positive integer K, such that: a*b*c*d=PK, and: a+b+c+d=PP-5. Find the minimum value of such a four-digit number and explain why.
对于四位数：\overline{abcd}，若存在质数P和正整数K，使得：a*b*c*d=PK，且：a+b+c+d=PP-5．求这样的四位数的最小值，并说明理由．
<result>1_399</result>