Immediately after 1989, write a series of numbers. The numbers written are all the single digits of the product of the two numbers in front of them. For example, 8*9=72, write 2 after 9, 2*9=18, write after 2 8, ..., get a string of numbers in this way, starting from 1, what is the 1989th number.
紧接着1989后面写一串数字，写下的数字都是它们前面两个数字之积的个位数，例如8*9=72，在9后面写2，2*9=18，在2后面写8，…，这样得到一串数字，从1开始，第1989个数字是多少．
<result>8</result>