Fill in a 3*3 grid table with nine numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9. Only one number is filled in each grid. Now put the largest number in each row The squares with the smallest number are colored red, and the squares with the smallest number are colored green. Suppose M is the minimum number in the red grid, and m is the maximum number in the green grid, how many different values can Mm take.
在一个3*3的方格表中填有1，2，3，4，5，6，7，8，9九个数，每格中只填一个数，现将每行中放有最大数的格子染成红色，最小数的格子染成绿色．设M是红格中的最小数，m是绿格中的最大数，则M-m可以取到多少个不同的值．
<result>8</result>