Go: package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"strconv"
	"strings"
)

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

type Color int

const (
	ColorBlack Color = iota
	ColorRed
)

var strByColor = map[Color]string{
	ColorBlack: "black",
	ColorRed:   "red",
}

func (c Color) String() string {
	return strByColor[c]
}

type Node struct {
	ID      int
	X, Y    int
	Color   Color
	NextIDs map[int]struct{}
}

func (n *Node) String() string {
	d, _ := json.Marshal(n)
	return string(d)
}

type Map struct {
	Width, Height int
	Nodes         map[int]*Node
}

func (m *Map) GetByID(id int) *Node {
	return m.Nodes[id]
}

func (m *Map) Get(x, y int) *Node {
	return m.Nodes[m.getID(x, y)]
}

func (m *Map) SetColor(x, y int, c Color) {
	m.Nodes[m.getID(x, y)].Color = c
}

func (m *Map) getID(x, y int) int {
	return x + y*m.Width
}

func (m *Map) init() {
	for x := 1; x <= m.Width; x++ {
		for y := 1; y <= m.Height; y++ {
			id := m.getID(x, y)
			m.Nodes[id] = &Node{ID: id, X: x, Y: y}
		}
	}
	for x := 1; x <= m.Width; x++ {
		for y := 1; y <= m.Height; y++ {
			nextIDs := map[int]struct{}{}
			if x > 1 {
				nextIDs[m.getID(x-1, y)] = struct{}{}
			}
			if x < m.Width {
				nextIDs[m.getID(x+1, y)] = struct{}{}
			}
			if y > 1 {
				nextIDs[m.getID(x, y-1)] = struct{}{}
			}
			if y < m.Height {
				nextIDs[m.getID(x, y+1)] = struct{}{}
			}
			m.Get(x, y).NextIDs = nextIDs
		}
	}
}

func NewMap(w, h int) *Map {
	m := &Map{Width: w, Height: h, Nodes: map[int]*Node{}}
	m.init()
	return m
}

type Searcher struct {
	Map        *Map
	queue      []*Node
	touchedIDs map[int]struct{}
	visitedIDs map[int]struct{}
}

func NewSearcher(m *Map) *Searcher {
	return &Searcher{
		Map:        m,
		queue:      []*Node{},
		touchedIDs: map[int]struct{}{},
		visitedIDs: map[int]struct{}{},
	}
}

func (s *Searcher) Search(start *Node) {
	s.enqueue(start)

	for {
		if len(s.queue) == 0 {
			break
		}
		for nextID := range s.dequeue().NextIDs {
			n := s.Map.GetByID(nextID)
			if n.Color == ColorRed || s.hasTouched(n) {
				continue
			}
			s.enqueue(n)
		}
	}
}

func (s *Searcher) VisitedNodeCount() int {
	return len(s.visitedIDs)
}

func (s *Searcher) hasTouched(n *Node) bool {
	_, ok := s.touchedIDs[n.ID]
	return ok
}

func (s *Searcher) enqueue(n *Node) {
	s.queue = append(s.queue, n)
	s.touchedIDs[n.ID] = struct{}{}
}

func (s *Searcher) dequeue() *Node {
	n := s.queue[0]
	s.queue = s.queue[1:]
	s.visitedIDs[n.ID] = struct{}{}
	return n
}

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])

		m := NewMap(w, h)

		// Set colors
		var start *Node
		for y := 1; y <= h; y++ {
			sc.Scan()
			for i, c := range sc.Text() {
				switch c {
				case '.', '@':
					m.SetColor(i+1, y, ColorBlack)
					if c == '@' {
						start = m.Get(i+1, y)
					}
				case '#':
					m.SetColor(i+1, y, ColorRed)
				}
			}
		}

		// Search
		s := NewSearcher(m)
		s.Search(start)
		fmt.Println(s.VisitedNodeCount())
	}
}

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;
}