Problem Statement

K, whose hobby is studying communist and socialist countries, has decided to make a flag to decorate a booth at the Ohashi Technical College cultural festival.

The flag is divided into a grid of N rows and M columns.

He wants to paint the entire flag red.
However, an arbitrary number of arbitrary cells of the flag have already been painted red.
How many cells need to be painted in order to make all cells of the flag red?

Input

$N\ M$
$A_1$
$\dots$
$A_N$

The first line contains two integers N, M (3 ≦ N ≦ 50, 3 ≦ M ≦ 50) separated by a space. This means that the flag is divided into a grid of N rows and M columns.

Each of the following N lines contains a string of M characters, representing the colors painted on the cells of the flag. The j-th character (1 ≦ j ≦ M) of the i-th of these N lines (1 ≦ i ≦ N) is either 'W' or 'R', representing the color of the cell at row i, column j of the old flag's grid. 'W' represents white and 'R' represents red.

Output

Output a single line.
Output the minimum number of cells that must be painted in order to make all cells of the NxM flag red.

Sample

3 3
WRW
RWR
WRW

5

8 5
RRRRR
RRRRR
RRRRR
RRRRR
RRRRR
RRRRR
RRRRR
RRRRR

0