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>
using namespace std;

const int NUM = 7;

void grooping(int y, int x, int w, int h, char** room, unsigned long*** group, unsigned long* next)
{
	if (room[y][x] != '#') {
		for (int i = y - 1; i <= y + 1; i++) {
			for (int j = x - 1; j <= x + 1; j++) {
				if (i < 0 || j < 0 || i >= h || j >= w) {
					continue;
				}
				if ((i == y && j != x) || (i != y && j == x)) {
					for (int k = 0; k < NUM; k++) {
						group[y][x][k] |= group[i][j][k];
					}
				}
			}
		}
		for (int i = 0; i < NUM; i++) {
			if (group[y][x][i] == 0UL && next[i] != 0UL) {
				group[y][x][i] |= next[i];
				next[i] <<= 1;
				break;
			}
		}
	}
}

int main()
{
	int w, h;
	while (true) {
		cin >> w >> h;
		if (w == 0 && h == 0) {
			break;
		}

		unsigned long next[NUM] = { 1UL, 1UL, 1UL, 1UL, 1UL, 1UL, 1UL };
		char** room = new char*[h];
		unsigned long*** group = new unsigned long**[h];
		int x, y;
		for (int i = 0; i < h; i++) {
			room[i] = new char[w];
			group[i] = new unsigned long*[w];
			for (int j = 0; j < w; j++) {
				cin >> room[i][j];
				if (room[i][j] == '@') {
					x = j;
					y = i;
				}
				group[i][j] = new unsigned long[NUM];
				for (int k = 0; k < NUM; k++) {
					group[i][j][k] = 0UL;
				}
			}
		}

		for (int k = 0; k < 2; k++) {
            bool flag=true;
			for (int i = 0; i >= 0; (flag ? i++ : i--)) {
				for (int j = 0; j >=0 ; (flag ? j++ : j--)) {
					grooping(i, j, w, h, room, group, next);
                    if (i==h-1 && j==w-1) {
                        flag=!flag;
                    }
				}
			}
			for (int j = 0; j >= 0; flag ? j-- : j++) {
				for (int i = 0; i >= 0; flag ? i-- : i++) {
					grooping(i, j, w, h, room, group, next);
                    if (i==h-1 && j==w-1) {
                        flag=!flag;
                    }
				}
			}
		}

		int count = 0;
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				for (int k = 0; k < NUM; k++) {
					if ((group[i][j][k] & group[y][x][k]) != 0UL) {
						count++;
						break;
					}
				}
			}
		}

		cout << count << '\n';

		for (int i = 0; i < h; i++) {
			delete[] room[i];
			for (int j = 0; j < w; j++) {
				delete[] group[i][j];
			}
			delete[] group[i];
		}
		delete[] room;
		delete[] group;
	}

	return 0;
}

C++: #include <iostream>
using namespace std;
int w,h;
int tx[4] = {0,-1,0,1};
int ty[4] = {-1,0,1,0};
char map[21][21];

int slv(int x,int y){
    map[y][x]='#';
    int ans=0;
    for(int i=0;i<4;++i)
        if( x+tx[i]!=-1 || y+ty[i]!=-1 || x+tx[i]!=w || y+ty[i]!=h)
            if( map[y+ty[i]][x+tx[i]] == '.' )
                ans+=slv( x+tx[i], y+ty[i] ) + 1 ;
    return ans;
}

int main()
{
    int ix,iy;
    while(1){
        cin >> w >> h;
        if(w==0&&h==0)break;
        for(int i=0;i<h;++i)
            for(int j=0;j<w;++j){
                cin >> map[i][j];
                if(map[i][j]=='@'){ix=j;iy=i;}
            }
        cout << slv( ix , iy ) + 1 << endl;
    }
    return 0;
}

C++: #include<bits/stdc++.h>
#define LL long long
#define REP(i,n) for(int i=0;i<(n);++i)
#define REPA(i,n) for(int i=1;i<(n);++i)
#define foreach(i, n) for(auto &i:(n))
#define PII pair<int,int>
#define PLI pair<long long, int>
#define PLL pair<long long, long long>
#define PDD pair<double, double>
#define MOD ((int)1e9 + 7)
#define INF ((int)1e9)
#define INFLL ((LL)1e18)
#define ALL(x) (x).begin(),(x).end()
#define ctoi(x) (x - 'a') 
#define CTOI(x) (x - 'A')
#define BIT(x) (1 << (x))
using namespace std;

LL modinv(LL a){
    LL b = MOD, u = 1, v = 0;
    while(b){
        LL t = a / b;
        a -= t * b;swap(a, b);
        u -= t * v;swap(u, v);
    }
    u%=MOD;
    if(u < 0) u += MOD;
    return u;

}

LL exp(LL a, LL b){
    LL sum = a;
    LL res = 1;
    while(b){
        if(b&1){
            res = (res * sum)%MOD;
        }
        sum = (sum * sum) % MOD;
        b>>=1;
    }
    return res;
}

int N, M;
vector<string> tail;
int mx[]={1, 0, -1, 0}, my[]={0, 1, 0, -1};

int main(){
    while(cin>>N>>M&&N){
        tail.assign(M, "");
        foreach(i, tail)cin>>i;
        int fx, fy;
        REP(i, M){
            REP(j, N){
                if(tail[i][j]=='@'){
                    fy=i;
                    fx=j;
                    tail[i][j]='#';
                    break;
                }
            }
        }
        int ans = 1;
        queue<PII> que;
        que.push(PII(fy, fx));
        while(!que.empty()){
            PII d = que.front();
            que.pop();
            REP(i, 4){
                int ny = d.first + my[i];
                int nx = d.second + mx[i];
                if(nx==-1||ny==-1||nx==N||ny==M||tail[ny][nx]=='#')continue;
                ++ans;
                tail[ny][nx]='#';
                que.push(PII(ny, nx));
            }
        }
        cout << ans << endl;
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
typedef pair<int,int> P;
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
int w,h;
char ma[30][30];
int b[30][30];
int cnt;
int dfs(int sy,int sx){
    for(int i=0;i<4;i++){
        int ny=sy+dy[i],nx=sx+dx[i];
        if(ny < 0 || ny > h - 1 || nx < 0 || nx > w - 1 || b[ny][nx]==1 || ma[ny][nx]=='#'){continue;}
        b[ny][nx]=1;
        cnt++;
        dfs(ny,nx);
    }
    return cnt;
}
int main(){
    while(1){
        cin>>w>>h;
        if(w==0 && h==0){
            break;
        }
        int sx,sy;
        for(int i=0;i<h;i++){
            for(int j=0;j<w;j++){
                cin>>ma[i][j];
                if(ma[i][j]=='@'){
                    sy=i;
                    sx=j;
                }
            }
        }
        cnt=1;
        for(int i=0;i<h;i++){
            for(int j=0;j<w;j++){
                b[i][j]=0;
            }
        }
        b[sy][sx]=1;
        cout<<dfs(sy,sx)<<endl;
    }
    return 0;
}