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 <iostream>
using namespace std;

char a[22][22];
int w, h;
int yy[4] = {-1, 0, 0, 1}, xx[4] = {0, 1, -1, 0};
int solve(int y, int x){
	if(a[y][x] == '#')return 0;
	a[y][x] = '#';
	int ans = 0;
	for(int i = 0;i < 4;i++){
		ans += solve(y+yy[i], x+xx[i]);
	}
	return ans+1;
}

int main(){
	int y, x;
	while(cin >> w >> h, w){
		fill((char*)a, (char*)(a+22), '#');
		for(int i = 1;i <= h;i++)
		for(int j = 1;j <= w;j++){
			cin >> a[i][j];
			if(a[i][j] == '@'){y = i;x = j;}
		}
		cout << solve(y, x) << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
using namespace std;

#define REP(i, b, n) for (int i = (b); i < (n); i++)
#define rep(i, n) REP(i, 0, n)

#define IS_IN_RANGE(x, w, y, h) ((0 <= x) && (x < w) && (0 <= y) && (y < h))

#define MAX 21
int w, h;
char brd[MAX][MAX];

int sx, sy;

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

int solve(int y, int x)
{
	if (!IS_IN_RANGE(y, h, x, w)) return 0;
	if (brd[y][x] == '#') return 0;
	brd[y][x] = '#';
	int ans = 1;
	rep(i, 4)
		ans += solve(y+dy[i], x+dx[i]);
	return ans;
}

int main()
{
	while (cin >> w >> h, w|h) {
		rep(j, h) rep(i, w) {
			cin >> brd[j][i];
			if (brd[j][i] == '@') {
				sy = j, sx = i;
				brd[j][i] = '.';
			}
		}
		cout << solve(sy, sx) << endl;
	}
	return 0;
}

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

const int dx[] = {1,0,-1,0};
const int dy[] = {0,-1,0,1};
int W,H;
int q[22][22] = {};
char p[22][22];

int main() {
	queue<pair<int,int> > M;
	while(cin >> W >> H){
		if (W == 0) return 0;
		int count = 0;
		for (int i = 1; i <= H; i++){
			for (int j = 1; j <= W; j++){
				cin >> p[i][j];
				if (p[i][j] == '@' ){
					M.push(make_pair(i,j));
					count = 1;
					q[i][j] = 1;
				}
			}
		}
		while(!M.empty()){
			W = M.front().first;
			H = M.front().second;
			M.pop();
			for (int i = 0; i <= 3; i++)
			{		
				if (p[W+dx[i]][H+dy[i]] == '.' && q[W+dx[i]][H+dy[i]] == 0)
				{
					M.push(make_pair(W + dx[i], H + dy[i]));
					q[W + dx[i]][H + dy[i]] = 1;
					count += 1;
				}
			}
		}
		cout << count << endl;
	}
}

C++: #include<iostream>
#include<vector>
#include<cstdio>
#include<string>
#include<algorithm>
#include<numeric>
#include<map>
#include<math.h>

using namespace::std;

char gMap[22][22];
bool MapFlg[22][22];
int gRedCount;
void initMap(void)
{
  for(int i = 0; i < 22; i++)
    {
      for(int j = 0; j < 22; j++)
	{
	  gMap[i][j] = '#';
	  MapFlg[i][j] = false;
	}
    }
  gRedCount = 0;
}

void showMap(void)
{
  for(int i = 0; i < 22; i++)
    {
      for(int j = 0; j < 22; j++)
	{
	  cout << gMap[i][j];
	}
      cout << endl;
    } 
}

int countMap(int x , int y)
{
  int dx[] = { 0  , 1 , -1 , 0 };
  int dy[] = { -1 , 0 ,  0 , 1 };

  for(int i = 0; i < 4; i++)
    {
      int mx = x + dx[i];
      int my = y + dy[i];

      if( gMap[my][mx] != '@' && gMap[my][mx] != '#' && MapFlg[my][mx] == false)
	{
	  gRedCount++;
	  MapFlg[my][mx] = true;
	  countMap(mx , my);
	}
    }

  return gRedCount;

}

void calcAns(int sx, int sy)
{
  cout << countMap(sx,sy) + 1 << endl;
}

int main(void)
{

  int w,h;

  while( cin >> w >> h  && (w != 0 && h != 0))
    {
      int sx,sy;
      initMap();
      for(int i = 1; i <= h; i++)
	{
	  for(int j = 1; j <= w; j++)
	    {
	      cin >> gMap[i][j];
	      if( gMap[i][j] == '@')
		{
		  sy = i;
		  sx = j;
		}
	    }
	}
      calcAns(sx,sy);
    }

  return 0;
}

C++: #include<cstdio>
#include<cstdlib>
#include<iostream>
#include<string>
#include<map>
#include<vector>
#include<algorithm>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

using namespace std;
int ans = 0;

void bfs(char **tile, int w, int h){
  ans++;
  tile[w][h] = '#';

  if(tile[w][h-1] == '.')
  bfs(tile, w, h-1);

  if(tile[w][h+1] == '.')
  bfs(tile, w, h+1);

  if(tile[w-1][h] == '.')
  bfs(tile, w-1, h);

  if(tile[w+1][h] == '.')
  bfs(tile, w+1, h);

  return;
}


int main(){
  int W,H,index_w,index_h;

  while(true){
    cin >> W >> H;
    if(W == 0 && H == 0) break;

    char **tile;
    tile = new char* [H+2];
    REP(i,H+2) tile[i] = new char[W+2];

    REP(i,H+2){
      REP(j,W+2){
        if(i == 0 || i == H+1 || j == 0 || j == W+1) tile[i][j] = '#'; //sentry?
        else scanf(" %c",&tile[i][j]);

        if(tile[i][j] == '@') {
          index_h = j;
          index_w = i;
        }

      }
    }
    ans = 0;
    bfs(tile,index_w,index_h);
    
    REP(i,H) delete[] tile[i];
    delete[] tile;
    
    cout << ans << endl;
  }
  return 0;
}