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 <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <string>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>

#define rep(i,j) REP((i), 0, (j))
#define REP(i,j,k) for(int i=(j);(i)<(k);++i)
#define between(a,x,b) ((a)<=(x)&&(x)<=(b))
#define ck(i, j) ((i) >= 0 && (i) < (j))
using namespace std;
char tile[21][21];
int  w, h, dy[] = {-1,0,1,0}, dx[] = {0,-1,0,1};

int dfs(int y, int x){
  tile[y][x] = '#';
  int res = 1;
  rep(i, 4){
    int ny = y+dy[i], nx = x+dx[i];
    if(ck(ny, h) && ck(nx, w) && tile[ny][nx] == '.')
      res += dfs(ny, nx);
  }

  return res; 
}

int main(){
  while(scanf("%d%d", &w, &h) && w && h){
    rep(i, h)  scanf("%s", tile[i]);
    rep(i, h) rep(j, w)
      if(tile[i][j] == '@') printf("%d\n", dfs(i, j));
  } 
  return 0;
}

C++: #include <stdio.h>
int x,y,p,q,i,w,h,r=1;
int j,k[101][101];
char s[101][101];
int a[]={1,-1,0,0}, b[]={0,0,1,-1};
void func(int x, int y){
    for(i=0;i<4;i++){
        if (x+a[i]<=h&&x+a[i]>0&&y+b[i]<=w&&y+b[i]>0){
            if(s[x+a[i]][y+b[i]]=='.'){
                r++;
                k[x+a[i]][y+b[i]]=1;
                func(x+a[i],y+b[i]);
            }
            
        }
    }
}

int main(){
        while(1){
        scanf("%d %d",&w,&h);
        if (w==0&&h==0) break;
        for (i=1;i<=h;i++){
            for (j=1;j<=w;j++){
                scanf("%c",&s[i][j]);
                if (s[i][j]=='@') k[i][j]=1;
                else k[i][j]=0;
                if (s[i][j]=='@') {
                    p=i; q=j;
                }
            }
        }
        func(p,q);
        printf("%d\n",r);
        
    }
    return 0;
}

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

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

vector<string> m;
int ans = 0;

void dfs(int x, int y){
  m[y][x] = '#';
  ans++;
  for(int i=0; i<4; i++){
    int nx = x + dx[i];
    int ny = y + dy[i];
    if(nx >= w || nx < 0 || ny >= h || ny < 0) continue;
    if(m[ny][nx] == '.'){
      dfs(nx,ny);
    }
  }
}


int main(){

  while(1){
    cin >> w >> h;
    if(!w and !h) break;
    m.clear();
    
    for(int i=0; i<h; i++){
      string s; cin >> s;
      m.push_back(s);
    }

    int sx,sy;
    for(int i=0; i<h; i++){
      for(int j=0; j<w; j++){
	if(m[i][j] == '@'){
	  sx = j;
	  sy = i;
	}
      }
    }
    ans =0;
    dfs(sx,sy);
    cout << ans <<  endl;

  }

}

C++: #include <bits/stdc++.h>
using namespace std;

#define ll long long
#define vvi vector<vector<int>>
#define vec vector
#define pq priority_queue
#define all(v) (v).begin(), (v).end()
#define rep(i, n) for (int (i) = (0); (i) < (n); ++(i))
#define repp(i, m, n) for (int (i) = (m); (i) < (n); ++(i))
#define debug(x) cerr << #x << ": " << x << endl;
#define debug2(x, y) cerr<<"("<<#x<<", "<<#y<<") = "<<"("<<x<<", "<<y<<")"<<endl;
#define debug3(x, y, z) cerr<<"("<<#x<<", "<<#y<<", "<<#z<<") = "<<"("<<x<<", "<<y<<", "<<z<<")"<<endl;
#define debugB(x, y) cerr<<#x<<": "<<bitset<y>(x) << endl;
#define line() cerr << "---------------" << endl;

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

template<typename T>
void printA(vector<T> &printArray, char between = ' ') {
   int paSize = printArray.size();
   for (int i = 0; i < paSize; i++) { cerr << printArray[i] << between;}
   if (between != '\n') {cerr << endl;}
}

// ------------------------------------------------------------------------------------------

int W, H;
char B[30][30];

int dfs(int y, int x) {
   int ret = 1;
   B[y][x] = '#';
   rep (i, 4) {
      int nx = x + dx[i], ny = y + dy[i];
      if (nx < 0 || nx >= W || ny < 0 || ny >= H || B[ny][nx] == '#') continue;
      ret += dfs(ny, nx);
   }
   return ret;
}

void solve() {
   rep (i, H) {
      cin >> B[i];
   }
   rep (i, H) {
      rep (j, W) {
         if (B[i][j] == '@') {
            cout << dfs(i, j) << endl;
            return;
         }
      }
   }
}

int main() {
   while (1) {
      cin >> W >> H;
      if (H*W == 0) break;
      solve();
   }

   return 0;
}

C++: /*********
深さ優先探索
**********/

#include<iostream>
#include<cstdio>
#include<algorithm>

void saiki(int xx,int yy);

int x,y;
int ans=0;
char tail[20][20]={};
int i,j;



int main(){
  
  while(1){
  scanf("%d %d",&x,&y);
  if(x==0 && y==0);
  for(i=0;i<y;i++) scanf("%s",tail[i]);
  
  for(i=0;i<y;i++){
    for(j=0;j<x;j++){
      if(tail[i][j]=='@'){
	saiki(j,i); break;
      }
    }
  }

  printf("%d\n",ans);
  ans=0;
  }
  
  return 0;
}


void saiki(int xx,int yy){

  ans++;
  tail[yy][xx]='#';

  int ny=yy-1,nx=xx;
  if(0<=nx && nx<x && 0<=ny && ny<y && tail[ny][nx]=='.') saiki(nx,ny);//水たまりだったら再起
  ny=yy,nx=xx-1;
  if(0<=nx && nx<x && 0<=ny && ny<y && tail[ny][nx]=='.') saiki(nx,ny);
  ny=yy,nx=xx+1;
  if(0<=nx && nx<x && 0<=ny && ny<y && tail[ny][nx]=='.') saiki(nx,ny);
  ny=yy+1,nx=xx;
  if(0<=nx && nx<x && 0<=ny && ny<y && tail[ny][nx]=='.') saiki(nx,ny);

}

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

int w, h;
char tile[20][20];
int cnt = 0;
int dx[4] = { 1, -1, 0, 0 };
int dy[4] = { 0, 0, 1, -1 };

void f(int x, int y){
	tile[x][y] = '#';
	cnt++;
	for (int i = 0; i < 4; i++){
		int X = x + dx[i];
		int Y = y + dy[i];
		if (tile[X][Y] != '#' && 0 <= X && X < w && 0 <= Y && Y < h){
			f(X, Y);
		}
	}
}

int main(){

	while (cin >> w >> h, w + h != 0){
		cnt = 0;
		for (int y = 0; y < h; y++){
			for (int x = 0; x < w; x++){
				cin >> tile[x][y];
			}
		}

		for (int y = 0; y < h; y++){
			for (int x = 0; x < w; x++){
				if (tile[x][y] == '@') f(x, y);
			}
		}

		cout << cnt << endl;
	}

	return 0;
}