There is a "digital black hole" game: randomly select four different numbers to form a largest four-digit number and a smallest four-digit number, and subtract the decimal from the large number. Repeat the above process with four digits of the obtained four-digit number, and after several steps of calculation, 6174 will be obtained. Please give it a try, choose the four numbers 1, 2, 5, 6, how many steps you can get 6174.
有一个"数字黑洞"的游戏：任意选四个不同的数字，组成一个最大的四位数和一个最小的四位数，用大数减去小数．用所得的四位数中的四个数字重复上述过程，经过几步运算，必得6174．请你试一试，选择1，2，5，6四个数字，经过多少步运算可得到6174．
<result>5</result>