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 <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <bitset>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;
typedef long long ll;
typedef pair<int,int> pint;
typedef vector<int> vint;
typedef vector<pint> vpint;
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for (int i=(n)-1;i>=0;i--)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define REPS(i,f,n) for (int i=(f)-1;i>=(n);i--)
int dx[4] = {1, 0, 0, -1};
int dy[4] = {0, 1, -1, 0};

char board[21][21];
int w, h;
int x, y;// ?????¨?????????

void slove(void){
	int cnt = 0;
	queue<pint> q;
	q.push(make_pair(y, x));//?????¨????????????queue?????\??????

	while(!q.empty()){
		pint now = q.front(); q.pop();
		rep(i, 4){
			int nowy = now.fi + dy[i];
			int nowx = now.se + dx[i];
			if (0 <= nowy <= h - 1 && 0 <= nowx && nowx <= w - 1){
				if (board[nowy][nowx] == '.'){
					cnt++;
					printf("%d\n", cnt);
					board[nowy][nowx] = 0;
					q.push(make_pair(nowy, nowx));
				}
			}
		}
	}
	printf("%d\n", cnt + 1);//?§?????????´????????\??????
	return;
}

void scan(int w, int h){
	rep(i, h){
		rep(j, w){
			cin >> board[i][j];
			if (board[i][j] == '@'){
				y = i; x = j;
			}
		}
		getchar();
	}
	/*
	rep(i, h){
		rep(j, w){
			printf("%c", board[i][j]);
		}
		printf("\n");
	}
	*/
	slove();
	return;
}

int main(void){
	rep(i, 1000){
		cin >> w >> h;

		if (w == 0) break;
		scan(w, h);
	}
	return 0;
}

C++: #include <iostream>
#define MAX 22
using namespace std;

int counter = 0;
char tile[MAX][MAX];

void redtile(int y, int x){
	tile[y][x] = '+';
	counter++;
	if (x + 1 < MAX && tile[y][x + 1] == '.')
		redtile(y, x + 1);
	if (x - 1 >= 0 && tile[y][x - 1] == '.')
		redtile(y, x - 1);
	if (y + 1 < MAX&&tile[y + 1][x] == '.')
		redtile(y + 1, x);
	if (y - 1 >= 0 && tile[y - 1][x] == '.')
		redtile(y - 1, x);
}


int main()
{
	int w, h, initi, initj;
	while (cin >> w >> h, w || h){
		for (int i = 0; i < MAX; i++){
			for (int j = 0; j < MAX; j++){
				tile[i][j] = 0;
			}
		}
		for (int i = 0; i < h; i++){
			for (int j = 0; j < w; j++){
				cin >> tile[i][j];
				if (tile[i][j] == '@'){
					tile[i][j] = '.';
					initi = i;
					initj = j;
				}
			}
		}
		counter = 0;
		redtile(initi, initj);
		cout << counter << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
using namespace std;

int W, H;
char visit[21][21];
int dfs(int h, int w){
  int sum=1;
  if(0>w || w==W || 0>h || h==H) return 0;
  if(visit[h][w]=='#')  return 0;
  if(visit[h][w]=='!')   return 0;
    visit[h][w] = '!';
    sum += dfs(h, w+1);
    sum += dfs(h, w-1);
    sum += dfs(h+1, w);
    sum += dfs(h-1, w);
   
  return sum;
}

int main(void){
  int w1, h1;
  string str;
  while(cin >> W >> H){
    if(W == 0 && H == 0)  break;
    for(int i=0; i<H; i++){
      cin >> str;
      for(int j=0; j<W; j++){
        visit[i][j] = str[j];
        if(visit[i][j] == '@'){
          visit[i][j] = '.';
          w1 = j; h1 = i;  
        }
      }
    }
    cout << dfs(h1, w1) <<endl;
  }
   
  return 0;
}

C++: #include<iostream>
#include<string>
using namespace std;
int ans;
int w,h;
string map[40];
int vec[4][2]={{0,1},{0,-1},{-1,0},{1,0}};
void move(int x,int y){
	ans++;
	map[x][y]='#';
	for(int i=0;i<4;i++){
		if((x+vec[i][0]>=0)&&(y+vec[i][1]>=0)&&(x+vec[i][0]<h)&&(y+vec[i][1]<w)){
			if(map[x+vec[i][0]][y+vec[i][1]]=='.'){
				move(x+vec[i][0],y+vec[i][1]);
			}
		}
	}
	return;
}

int main(){
	while(cin>>w>>h,w){
		ans=0;
		int fx,fy;
		for(int i=0;i<h;i++){
			cin>>map[i];
		}
		for(int i=0;i<h;i++){
			for(int j=0;j<w;j++){
				if(map[i][j]=='@'){
					fx=i;
					fy=j;
					break;
				}
			}
		}
		move(fx,fy);
		cout<<ans<<endl;
		
	}
}

C++: #include <algorithm>
#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <map>
#define rep(i, n) for (int i=0; i<n; ++i)
#define FOR(i, a, b) for (int i=a; i<b; ++i)
#define pb(x) push_back(x)
#define ll long long
#define ul unsigned long long
#define dbg(x) cout  << #x << " : " << (x) << endl
#define out(x) cout << (x)
#define outl(x) cout << (x) << endl
#define int(n); int n; cin >> n;
#define long(n); long long n; cin >> n;
#define dbl(f); double f; cin >> f;
#define s(s); string s; cin >> s;
#define into(a, n) for (int i = 0; i < n; ++i) cin >> a[i]
using namespace std;

const int inf =1500000000;
char a[20][20];
int cnt; 
int w,h; 
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1}; 
void dfs(int x, int y) {
  a[y][x] = '#';
  cnt++;
  rep(i, 4) {
    int nx=x+dx[i];
    int ny=y+dy[i];
    if(nx<w&&ny<h&&nx>=0&&ny>=0&&a[ny][nx]=='.') dfs(nx, ny);
  }
}

int main () {
  while(true){
    cnt = 0;
    cin>>w>>h;
    if (w==0&& h==0) break;
    int x0,y0;
    rep(i, h) {
      rep(j, w) {
        cin>>a[i][j];
        if(a[i][j]=='@' ) {
          x0=j; y0=i;
          a[i][j]='.';
        }
      } 
    } 
    dfs(x0, y0);
    outl(cnt);
  }
  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <sstream>
#include <vector>
#include <string>
#include <queue>
#include <set>
#include <map>
#include <utility>
#include <algorithm>
#include <functional>

using namespace std;

#define rep(i,n) for((i)=0;(i)<(int)(n);(i)++)
#define each(c,itr) for(__typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)

int dx[] = {0,0,1,-1}, dy[] = {1,-1,0,0};

int w,h,res;
char field[30][30];

void dfs(int y, int x){
  int i;

  rep(i,4){
    int my = y + dy[i], mx = x + dx[i];
    if(0 <= my && 0 <= mx && my < h && mx < w && field[my][mx] != '#'){
      field[my][mx] = '#';
      res++;
      dfs(my,mx);
    }
  }
}

int main(){
  int i,j;

  while(true){
    scanf("%d %d",&w,&h);
    if(w == 0 && h == 0) break;
    res = 0;
    rep(i,h) scanf("%s",field[i]);
    rep(i,h) rep(j,w) if(field[i][j] == '@') dfs(i,j);
    printf("%d\n",res);
  }

  return 0;
}