Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

var (
	sc = bufio.NewScanner(os.Stdin)
)

type Color int

const (
	ColorBlack Color = iota
	ColorRed
)

type Node struct {
	ID    int
	X, Y  int
	Color Color
	Nexts []*Node
}

func main() {
	for sc.Scan() {
		if sc.Text() == "0 0" {
			break
		}
		chunks := strings.Split(sc.Text(), " ")
		w, _ := strconv.Atoi(chunks[0])
		h, _ := strconv.Atoi(chunks[1])

		// Initialize map
		m := map[int]map[int]*Node{}
		for x := 1; x <= w; x++ {
			m[x] = map[int]*Node{}
			for y := 1; y <= h; y++ {
				m[x][y] = &Node{ID: x + y*w, X: x, Y: y}
			}
		}
		for x := 1; x <= w; x++ {
			for y := 1; y <= h; y++ {
				nexts := []*Node{}
				if n, ok := m[x-1][y]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x][y-1]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x+1][y]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x][y+1]; ok {
					nexts = append(nexts, n)
				}
				m[x][y].Nexts = nexts
			}
		}

		// Set colors
		queue := []*Node{}
		touchedIDs := map[int]struct{}{}
		for y := 1; y <= h; y++ {
			sc.Scan()
			for i, c := range sc.Text() {
				switch c {
				case '.', '@':
					n := m[i+1][y]
					n.Color = ColorBlack
					if c == '@' {
						queue = append(queue, n)
						touchedIDs[n.ID] = struct{}{}
					}
				case '#':
					m[i+1][y].Color = ColorRed
				}
			}
		}

		// Search
		visitedIDs := map[int]struct{}{}
		for {
			if len(queue) == 0 {
				break
			}
			n := queue[0]
			queue = queue[1:]
			visitedIDs[n.ID] = struct{}{}
			for _, next := range n.Nexts {
				if next.Color == ColorRed {
					continue
				}
				if _, ok := touchedIDs[next.ID]; !ok {
					queue = append(queue, next)
					touchedIDs[n.ID] = struct{}{}
				}
			}
		}
		fmt.Println(len(visitedIDs))
	}
}

C++: #include <cstdio>
#include <cstring>
using namespace std;

int W, H;
char map[20][20];
int cnt;
int angle[][2] = {
	{-1, 0}, {0, -1}, {1, 0}, {0, 1}
};

void dfs(int x, int y)
{
	if (map[x][y] == '#' || x < 0 || y < 0 || x >= W || y >= H){
		return;
	}
	cnt++;
	map[x][y] = '#';
	
	for (int i = 0; i < 4; i++){
		dfs(x + angle[i][0], y + angle[i][1]);
	}
}

int main()
{
	int num;
	
	while (scanf("%d %d", &W, &H), W + H){
		int x;
		int y;
		memset(map, 0, sizeof(map));
		
		for (int i = 0; i < H; i++){
			for (int j = 0; j < W; j++){
				scanf(" %c", &map[j][i]);
				if (map[j][i] == '@'){
					x = j;
					y = i;
					map[j][i] = '.';
				}
			}
		}
		
		cnt = 0;
		dfs(x, y);
		
		printf("%d\n", cnt);
	}
	
	return 0;
}

C++: #include "bits/stdc++.h"
using std::cin;
using std::cout;

int cnt = 0;
char map[21][21];

void dfs(int x, int y, int mx, int my){
    if((x < 0) || (x >= mx)){
        return;
    }
    if((y < 0) || (y >= my)){
        return;
    }
    if(map[x][y] == '#'){
        return;
    }
    map[x][y] = '#';
    cnt++;
    dfs(x+1, y, mx, my);
    dfs(x-1, y, mx, my);
    dfs(x, y+1, mx, my);
    dfs(x, y-1, mx, my);
}

int main(){
    int W, H, sx, sy;
    cin >> W >> H;

    while(W != 0 && H != 0){
        for(int i = 0; i < H; i++){
            scanf("%20s", map[i]);
            if(std::string(map[i]).find('@') != std::string::npos){
                sx = i;
                sy = std::string(map[i]).find('@');
            }
        }
        dfs(sx, sy, H, W);
        cout << cnt << std::endl;

        cin >> W >> H;
        cnt = 0;
        
    }

C++: #include <bits/stdc++.h>
#define int long long
#define double long double
#define INF 1e18
using namespace std;
// x[H][W]
// 1: accessible
// INF: not arrived
// -1: can't access
int a[20][20];
int H, W;

void dfs(int x, int y) {
  int moveX[4] = { 1, 0, -1, 0 };
  int moveY[4] = { 0, 1, 0, -1 };
  a[y][x] = 1;
  for (int i = 0; i < 4; i++) {
    int nx = moveX[i]+x;
    int ny = moveY[i]+y;
    if (a[ny][nx] == INF && nx >= 0 && nx < W && ny >= 0 && ny < H) {
      dfs(nx, ny);
    }
  }
}

signed main() {
  while (cin>>W>>H, W+H!=0) {
    int startX, startY;
    for (int i = 0LL; i < H; i++) {
      for (int j = 0LL; j < W; j++) {
        char c; cin >> c;
        if (c == '.') {
          a[i][j] = INF;
        } else if (c == '#') {
          a[i][j] = -1;
        } else {
          a[i][j] = INF;
          startX = j;
          startY = i;
        }
      }
    }
    dfs(startX, startY);
    
    int ans = 0;
    for (int i = 0; i < H; i++) {
      for (int j = 0; j < W; j++) {
        if (a[i][j] == 1) ans++;
      }
    }

    cout << ans << endl;
  }
}

C++: #include<iostream>
#include<cstdio>
#include<string>
using namespace std;
#define loop(i,a,b) for(int i = a ; i < b ; i++)
#define rep(i,a) for(int i = 0 ; i < a ; i++) 

char maze[21][21];
int dx[4] = { 0, 0,-1, 1};
int dy[4] = {-1, 1, 0, 0};
int H,W;
bool inmaze(int x,int y){
  return (0<=x && x<H) && (0<=y && y<W);
}

int dfs(int x,int y){
  if(!inmaze(x,y))return 0;
  maze[x][y] = '#';
  int res = 1;
  rep(i,4){
    if(maze[x+dx[i]][y+dy[i]] == '.'){
      res += dfs(x+dx[i],y+dy[i]);
    }
  }
  return res;
}
int main(void){
  while(cin>>W>>H,H+W){
    int sx,sy;
    rep(i,H){
      string s;
      cin>>s;
      rep(j,W){
	maze[i][j] = s[j];
	if(s[j] == '@'){
	  sx = i;sy = j;
	}
      }
    }
    maze[sx][sy] = '.';
    cout<<dfs(sx,sy)<<endl;
  }
}

C++: #if 0
#endif

#include <iostream>
#include <string>
#include <set>
using namespace std;

struct pos
{
    int x;
    int y;
};
bool state[25][25];
int result = 1, width, height;

void tansaku(pos cur)
{
    // 右へ
    if (cur.x < width - 1 && state[cur.x + 1][cur.y])
    {
        state[cur.x + 1][cur.y] = false;
        result++;
        tansaku({.x = cur.x + 1, .y = cur.y});
    }
    // 左へ
    if (0 < cur.x && state[cur.x - 1][cur.y])
    {
        state[cur.x - 1][cur.y] = false;
        result++;
        tansaku({.x = cur.x - 1, .y = cur.y});
    }
    // 上へ
    if (0 < cur.y && state[cur.x][cur.y - 1])
    {
        state[cur.x][cur.y - 1] = false;
        result++;
        tansaku({.x = cur.x, .y = cur.y - 1});
    }
    // 下へ
    if (cur.y < height - 1 && state[cur.x][cur.y + 1])
    {
        state[cur.x][cur.y + 1] = false;
        result++;
        tansaku({.x = cur.x, .y = cur.y + 1});
    }
}

int main()
{
    while (cin >> width >> height && (width != 0 || height != 0))
    {
        result = 1;
        pos cur;

        for (int y = 0; y < height; y++)
        {
            string word;
            cin >> word;
            for (int x = 0; x < width; x++)
            {
                char c = word[x];
                if ('.' == c)
                {
                    state[x][y] = true;
                }
                else if ('@' == c)
                {
                    state[x][y] = false;
                    cur.x = x;
                    cur.y = y;
                }
                else if ('#' == c)
                {
                    state[x][y] = false;
                }
            }
        }
        tansaku(cur);
        cout << result << endl;
    }
}

C++: #include<iostream>
#include<vector>
#include<string>
#include<queue>
#include<map>
using namespace std;
typedef pair<int,int> P;
int dx[]={0,0,1,-1},dy[]={1,-1,0,0};
int h,w;
vector<string> s;
bool inf(int y,int x){
	return (y>=0&&y<h&&x>=0&&x<w)?true:false;
}
int bfs(int sy,int sx){
	int ret=0;
	queue<P> que;
	que.push(P(sy,sx));
	vector<vector<bool> > used(h,vector<bool>(w,false));
	while(!que.empty()){
		P t=que.front();
		que.pop();
		int y=t.first,x=t.second;
		if(used[y][x]){
			continue;
		}
		used[y][x]=true;
		ret++;
		for(int i=0;i<4;i++){
			int ny=dy[i]+y,nx=dx[i]+x;
			if(inf(ny,nx)&&!used[ny][nx]&&s[ny][nx]!='#'){
				que.push(P(ny,nx));
			}
		}
	}
	return ret;
}
int main(){
	
	
	while(cin>>w>>h,h||w){
		s=vector<string>(h);
		for(int i=0;i<h;i++){
			cin>>s[i];
		}
		int ans=0;
		for(int i=0;i<h;i++){
			for(int j=0;j<w;j++){
				if(s[i][j]=='@'){
					ans=bfs(i,j);
				}
			}
		}
		cout<<ans<<endl;
	}
	return 0;
}