There are two ways of re-forming:
1. While replacing, original line must not shift to right or left. In this case the answer is 1 (10 goes after 1, hence only 1 stays in it's place).
2. If original line can shift, then the answer is 8 (numbers from 2 to 9 doesn't move).

Both algorithm failed, maybe something is missing in problem statement?

What is the answer for 20? 1 or 2 or 3?

I've found the test..