Given a m*n grids, each grid with character x or o,
if the grid is connected to the grid of its left, right, up or down
with the same character, those grids are in the same area.
we would like to know what is the largest area in the grid with o's. 

For example:
8 8    <--- 8 rows and 8 columns
XXXOOOOO
XXXXXOOX
XXXXXXXX
XXOOOXXX
XXXXXOOO
XXXOOOOO
XOOOOOOO
XXXXXXXX

then you should output 15  , the area for one grid is 1.

The first line contains two integers M and N
In the next M rows , each row contains N characters of X or O

One integer which is the largest area with 'O's