Problem Description：

There is a rectangular room, covered with square tiles. Each tile is colored either red or black. A man is standing on a black tile. From a tile, he can move to one of four adjacent tiles. But he can't move on red tiles, he can move only on black tiles.

Write a program to count the number of black tiles which he can reach by repeating the moves described above.  

Input：

The input consists of multiple data sets. A data set starts with a line containing two positive integers W and H; W and H are the numbers of tiles in the x- and y- directions, respectively. W and H are not more than 20.

There are H more lines in the data set, each of which includes W characters. Each character represents the color of a tile as follows.

'.' - a black tile

'#' - a red tile

'@' - a man on a black tile(appears exactly once in a data set)

Output：

For each data set, your program should output a line which contains the number of tiles he can reach from the initial tile (including itself).  

Sample Input：

6 9

....#.

.....#

......

......

......

......

......

#@...#

.#..#.  

11 9

.#.........

.#.#######.

.#.#.....#.

.#.#.###.#.

.#.#..@#.#.

.#.#####.#.

.#.......#.

.#########.

...........

11 6

..#..#..#..

..#..#..#..

..#..#..###

..#..#..#@.

..#..#..#..

..#..#..#..

7 7

..#.#..

..#.#..

###.###

...@...

###.###

..#.#..

..#.#..

0 0

Sample Output：

45

59

6

13

程序代码：  

#include<stdio.h>
int w,h;
char s[25][25];
int dfs(int x,int y)
{
    if(x<0||x>=w||y<0||y>=h)
        return 0;
    if(s[x][y]=='#')
        return 0;
    else
    {
        s[x][y]='#';
        return 1+dfs(x-1,y)+dfs(x+1,y)+dfs(x,y-1)+dfs(x,y+1);
    }
}
int main()
{
    int i,j;
    while(scanf("%d %d",&h,&w)&&w!=0&&h!=0)
    {
        for(i=0;i<w;i++)
            scanf("%s",s[i]);
        for(i=0;i<w;i++)
        {
            for(j=0;j<h;j++)
            {
                if(s[i][j]=='@')
                    printf("%d\n",dfs(i,j));
            }
        }
    }
    return 0;
}