Here, we want to solve path planning for a mobile robot cleaning a rectangular
room floor with furniture.
Consider the room floor paved with square tiles whose size fits the cleaning
robot (1 × 1). There are 'clean tiles' and 'dirty tiles', and the robot can
change a 'dirty tile' to a 'clean tile' by visiting the tile. Also there
may be some obstacles (furniture) whose size fits a tile in the room. If there
is an obstacle on a tile, the robot cannot visit it. The robot moves to an
adjacent tile with one move. The tile onto which the robot moves must be
one of four tiles (i.e., east, west, north or south) adjacent to the tile
where the robot is present. The robot may visit a tile twice or more.
Your task is to write a program which computes the minimum number of
moves for the robot to change all 'dirty tiles' to 'clean tiles', if ever possible.

Input

The input consists of multiple maps, each representing the size and arrangement
of the room. A map is given in the following format.
w h
c11 c12 c13 ... c1w
c21 c22 c23 ... c2w
...
ch1 ch2 ch3 ... chw

The integers w and h are the lengths of the two sides of the floor of the room
in terms of widths of floor tiles. w and h are less than or equal to 20.
The character cyx represents what is initially on the tile with coordinates
(x, y) as follows.
'.' : a clean tile
'*' : a dirty tile
'x' : a piece of furniture (obstacle)
'o' : the robot (initial position)

In the map the number of 'dirty tiles' does not exceed 10. There is only one 'robot'.
The end of the input is indicated by a line containing two zeros.
SAMPLE INPUT
7 5
.......
.o....
.......
.....
.......
15 13
.......x.......
...o...x......
.......x.......
.......x.......
.......x.......
...............
xxxxx.....xxxxx
...............
.......x.......
.......x.......
.......x.......
......x......
.......x.......
10 10
..........
..o.......
..........
..........
..........
.....xxxxx
.....x....
.....x.*..
.....x....
.....x....
0 0

Output

 
For each map, your program should output a line containing the minimum
number of moves. If the map includes 'dirty tiles' which the robot cannot reach,
your program should output -1. 
SAMPLE OUTPUT
8
49
-1