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 <bits/stdc++.h>
using namespace std;
const int inf = 1001001001;


int w, h;
int a[20][20];
int sw, sh;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int D[20][20];
int Ans = 1;


int main()
{
    while(cin >> w, w != 0)
    {
        Ans = 1;
        cin >> h;
        
        for(int i = 0; i < 20; i++)
        {
            for(int j = 0; j < 20; j++)
            {
                D[i][j] = inf;
            }
        }
        
        for(int i = 0; i < h; i++)
        {
            for(int j = 0; j < w; j++)
            {
                char x;
                cin >> x;
                if(x == '.')
                {
                    a[j][i] = 1;
                }
                else if(x == '#')
                {
                    a[j][i] = 0;
                }
                else
                {
                    sw = j;
                    sh = i;
                    a[j][i] = 100;  //  ????????§?????????
                }
            }
        }
        queue< pair<int, int> > Q;
        pair<int, int> S;
        S = make_pair(sw, sh);
        Q.push(S);
        D[sw][sh] = 0;
        int k = 0;
        while(! Q.empty())
        {
            pair<int, int> cur = Q.front();
            Q.pop();
            int x = cur.first;
            int y = cur.second;
            for(int i = 0; i < 4; i++)
            {
                if(a[x+dx[i]][y+dy[i]] == 1 && 0 <= x+dx[i] && x+dx[i] < w && 0 <= y+dy[i] && y+dy[i] < h && D[x+dx[i]][y+dy[i]] == inf)    //  ????????????????¢????????????????????????????????????°???
                {
                    D[x+dx[i]][y+dy[i]] = D[x][y] + 1;
                    Ans = Ans + 1;
                    pair<int, int> T;
                    T = make_pair(x+dx[i], y+dy[i]);
                    Q.push(T);
                }
            }
        }
        cout << Ans << endl;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;
const int inf = 1001001001;


int w, h;
int a[20][20];
int sw, sh;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int D[20][20];
int Ans = 1;


int main()
{
    while(cin >> w, w != 0)
    {
        Ans = 1;
        cin >> h;
        
        for(int i = 0; i < 20; i++)
        {
            for(int j = 0; j < 20; j++)
            {
                D[i][j] = inf;
            }
        }
        
        for(int i = 0; i < h; i++)
        {
            for(int j = 0; j < w; j++)
            {
                char x;
                cin >> x;
                if(x == '.')
                {
                    a[j][i] = 1;
                }
                else if(x == '#')
                {
                    a[j][i] = 0;
                }
                else
                {
                    sw = j;
                    sh = i;
                    a[j][i] = 100;  //  ????????§?????????
                }
            }
        }
        queue< pair<int, int> > Q;
        pair<int, int> S;
        S = make_pair(sw, sh);
        Q.push(S);
        D[sw][sh] = 0;
        int k = 0;
        while(! Q.empty())
        {
            pair<int, int> cur = Q.front();
            Q.pop();
            int x = cur.first;
            int y = cur.second;
            for(int i = 0; i < 4; i++)
            {
                if(a[x+dx[i]][y+dy[i]] == 1 && 0 <= x+dx[i] && x+dx[i] < w && 0 <= y+dy[i] && y+dy[i] < h && D[x+dx[i]][y+dy[i]] == inf)    //  ????????????????¢????????????????????????????????????°???
                {
                    D[x+dx[i]][y+dy[i]] = D[x][y] + 1;
                    Ans = Ans + 1;
                    pair<int, int> T;
                    T = make_pair(x+dx[i], y+dy[i]);
                    Q.push(T);
                }
            }
        }
        cout << Ans << endl;
    }
}

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

#define FOR( i, m, n )  for( int (i) = (m); (i) < (n); (i)++ )
#define REP( i, n )     FOR( i, 0, n )
#define ALL( a )        (a).begin(), (a).end()             

#define F				first
#define S				second

int w, h, cnt = 0;

int solve( vector<vector<char>>& f, pair<int, int>& mp ) {

	if( mp.F - 1 >= 0 && f[mp.S][mp.F - 1] == '.' ) {
		cnt++;
		f[mp.S][mp.F - 1] = '#';
		solve( f, make_pair( mp.F - 1, mp.S ) );
	}
	if( mp.F + 1 < w && f[mp.S][mp.F + 1] == '.' ) {
		f[mp.S][mp.F + 1] = '#';
		cnt++;
		solve( f, make_pair( mp.F + 1, mp.S ) );
	}
	if( mp.S - 1 >= 0 && f[mp.S - 1][mp.F] == '.' ) {
		f[mp.S - 1][mp.F] = '#';
		cnt++;
		solve( f, make_pair( mp.F, mp.S - 1 ) );
	}
	if( mp.S + 1 < h && f[mp.S + 1][mp.F] == '.' ) {
		f[mp.S + 1][mp.F] = '#';
		cnt++;
		solve( f, make_pair( mp.F, mp.S + 1 ) );
	}
	return cnt;
}

int main() {

	while( 1 ) {
		cin >> w >> h; if( w == 0 && h == 0 ) break;
		
		pair<int, int> mp;
		vector<vector<char>> f;
		vector<char> tmp( w );
		REP( i, h ) {
			REP( j, w ) {
				cin >> tmp[j];
				if( tmp[j] == '@' ) { 
					mp.first = j;
					mp.second = i; 
					tmp[j] = '#';
					cnt++;
				}
			}
			f.push_back( tmp );
		}

		cout << solve( f, mp ) << endl;
		cnt = 0;
	}
}