/
确保只有一个k和s
mid("123442654Q1000GK5F1L1S003",find("K","123442654Q1000GK5F1L1S003")+1,find("S","123442654Q1000GK5F1L1S003")-find("K","123442654Q1000GK5F1L1S003")-1)
如果K和S的相对位置是不变的话: