In chinese checkers a piece can jump must meet two conditions：

1.There is no piece on the Jump-off point and the droppoint.Meanwhile,There is one and only one piece between the two points.

2.The only piece must be right in the middle of the two points.

For example,from a jump to b('a' is jump-off point,'b' is droppoint,'*' means piece in the position,'.'means no piece in the position).

the cases can jump: a*b a..*..b a.....*.....b

the cases cannot jump: a**b a.*..b a...*.*...b a.*...b

Now Given a one-dimensional checkerboard,how many times need to jump from a to b(No other movement but jump).