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 <stack>
#include <vector>
#include <map>

using namespace std;

void input_field(vector< vector< char > > &field, int w, int h);
int reach_tile_num(vector< vector< char > > &field);
pair< int, int> search_start(vector< vector< char > > &field);

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

int main(){
  int w, h;

  while(cin >> w >> h, w&&h){
    vector< vector< char > >field(w+2, vector< char >(h+2, 0));
    
    input_field(field, w+2, h+2);
    cout << reach_tile_num(field) << endl;
  }
}


void input_field(vector< vector< char > > &field, int w, int h){
  for(int y = 0; y < h; y++){
    for(int x = 0; x < w; x++){
      if(x == 0 || y == 0
         || x == w-1 || y == h-1){
	field[y][x] = '#';
      }else{
	cin >> field[y][x];
      }
    }
  }
}

int reach_tile_num(vector< vector< char > > &field){
  int sum = 0;
  pair< int, int > start, cur;
  stack< pair< int, int > > s;

  start = search_start(field);
  s.push(start);

  while(!(s.empty())){
    cur = s.top();
    s.pop();
    if(field[cur.second][cur.first] == '.'
       || field[cur.second][cur.first] == '@'){
      sum++;
      for(int i = 0; i < 4; i++){
        s.push(make_pair(cur.first+dx[i], cur.second+dy[i]));
	field[cur.second][cur.first] = '#';
      }
    }
  }
  return sum;
}

pair< int, int> search_start(vector< vector< char > > &field){
  for(int y = 0; y < field.size(); y++){
    for(int x = 0; x < field[y].size(); x++){
      if(field[y][x] == '@') return make_pair(x,y);
    }
  }
}

C++: #include "bits/stdc++.h"

using namespace std;

typedef long long ll;
typedef pair<int, int> P;
typedef vector<int> VI;
typedef vector<VI> VVI;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const int INF = numeric_limits<int>::max() / 2;
const int NEG_INF = numeric_limits<int>::min() / 2;
const int MOD = 1e9 + 7;

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

    int w,h;
    int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};
    while(cin>>w>>h,w||h){
        vector< vector<int> > field(h,vector<int>(w,1));
        int x,y;
        for(int i=0;i<h;i++){
            string s;cin>>s;
            for(int j=0;j<w;j++){
                if(s[j]=='.') field[i][j]=0;
                else if(s[j]=='@'){x=i;y=j;}
            }
        }
        queue<P> q;
        q.push(P(x,y));
        int res=0;
        while(!q.empty()){
            P p=q.front();q.pop();
            for(int i=0;i<4;i++){
                int nx=p.first+dx[i],ny=p.second+dy[i];
                if(nx<0||h<=nx||ny<0||w<=ny) continue;
                if(field[nx][ny]==1) continue;
                res++;
                field[nx][ny]=1;
                q.push(P(nx,ny));
            }
        }
        cout<<res+1<<endl;
    }
}

C++: #include<stdio.h>
#include<string.h>
char m[22][22],*p;
int F(int x,int y)
{
	if(m[y][x]=='#')return 0;
	m[y][x]='#';
	return 1+F(x+1,y)+F(x-1,y)+F(x,y+1)+F(x,y-1);
}
int main()
{
	int w,h,i,x,y;
	while(scanf("%d%d",&w,&h),w)
	{
		for(i=1;i<=h;++i)
		{
			scanf("%s",m[i]+1);
			if(p=strchr(m[i]+1,'@'))x=p-m[y=i];
		}
		for(i=0;i<h+2;++i)m[i][0]=m[i][w+1]='#';
		for(i=0;i<w+2;++i)m[0][i]=m[h+1][i]='#';
		printf("%d\n",F(x,y));
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<n;i++)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

int w,h;
int sx,sy;

void solve(){
    vector<string> t(h);
    rep(i,h) cin >> t[i];

    rep(i,h) rep(j,w) if(t[i][j]=='@'){
        sx = i;
        sy = j;
        break;
    }

    bool visited[32][32];
    rep(i,32) rep(j,32) visited[i][j]=false;
    visited[sx][sy]=true;
    queue<pii> que;
    que.push(pii(sx,sy));
    while(!que.empty()){
        auto p = que.front();
        que.pop();

        int x = p.fi;
        int y = p.se;

        rep(i,4){
            int nx = x + dx[i];
            int ny = y + dy[i];
            if(nx<0 or ny<0 or nx>=h or ny>=w) continue;
            if(t[nx][ny]=='#') continue;
            if(visited[nx][ny]) continue;

            visited[nx][ny] = true;
            que.push(pii(nx,ny));
        }
    }

    int ans = 0;
    rep(i,h) rep(j,w) if(visited[i][j]) ans++;
    cout << ans << endl;
}

int main(){
    while(1){
        cin >> w >> h;
        if(w==0 and h==0) break;
        solve();
    }
}