Solitons (Solitary Waves)
-------------------------

Normal sound and water waves disperse over time, but a soliton is a
solitary wave that has a particular shape which reacts just perfectly
with the differential equation of the system, so that it is able to
maintain its shape and speed potentially forever. A theory related to
quantum string theory is that all fundamental particles, eg.
electrons, are solitons.  A pair of Japanese a few years ago modeled
simplified solitons by the following discrete system.

There is a line of 1000 cells, a number of which contain a single
ball and the rest are empty (similar to a Turing Machine).
Each time step t, each of the balls moves exactly once. They move one
at a time in the order that they appear left to right at time t. At
each of these sub-steps, the left most ball that has not yet moved
during this time step t, moves to the first empty cell to the
right. For example: Tape times t, t+1, and t+2 with balls numbered 

_ _ _ 1 2 3 _ _ 4
_ _ _ _ _ _ 1 2 _ 3 4
_ _ _ _ _ _ _ _ 1 _ _ 2 3 4

Input
-----
The input will contain multiple lines. Each line looks like the following:

20 b b b _ _ _ _ b 

indicating that for this run of the program, the number of time steps
that you should run the algorithm is t=20 and that at t=0 we have that
cell[0], cell[1], cell[2], and cell[7] each contain a ball and the
rest are empty.

Output 
------

The output is the contents of the cells up to and including the last ball.

Sample Input
------------

0 b b b _ _ _ _ b
1 b b b _ _ _ _ b
2 b b b _ _ _ _ b
3 b b b _ _ _ _ b
8 b b b _ _ _ _ b

Sample Output
-------------

b b b _ _ _ _ b
_ _ _ b b b _ _ b
_ _ _ _ _ _ b b _ b b
_ _ _ _ _ _ _ _ b _ _ b b b
_ _ _ _ _ _ _ _ _ _ _ _ _ b _ _ _ _ _ _ _ _ _ _ _ _ b b b