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++: // #define USE_CPP11
// #define USE_PRINTF

#include <iostream>
#include <iomanip>
#include <map>
#include <set>
#include <utility>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <numeric>
#include <complex>
#include <memory>
#include <sstream>

#ifdef USE_CPP11
#include <unordered_map>
#include <unordered_set>
#include <functional>
#endif

#define PRINT(obj) cout << obj << endl
#define REP(i, n) for(int (i) = 0; (i) < (n); i++)

typedef long long ll;

using namespace std;

namespace Scanner {
#ifdef USE_PRINTF
  int    nextInt()    { int    d; scanf("%d" , &d); return d; }
  float  nextFloat()  { float  f; scanf("%f" , &f); return f; }
  double nextDouble() { double f; scanf("%lf", &f); return f; }  
  string nextString() { string s; scanf("%s" , &s); return s; }
  ll     nextll()     { ll     l; scanf("%ll", &l); return l; }
#else
  int    nextInt()    { int    d; cin >> d; return d; }
  float  nextFloat()  { float  f; cin >> f; return f; }
  double nextDouble() { double f; cin >> f; return f; }  
  string nextString() { string s; cin >> s; return s; }
  ll     nextll()     { ll     l; cin >> l; return l; }
#endif

  string getLine() { 
    string input;
    getline(cin, input);
    return input;
  }
};

namespace myLibrary {
  vector<string> split(const string& str, char delim) {
    vector<string> ret;
    size_t current = 0, found;
    while ((found = str.find_first_of(delim, current)) != string::npos) {
      ret.push_back(string(str, current, found - current));
      current = found + 1;
    }
    ret.push_back(string(str, current, str.size() - current));
    return ret;
  }
  
#ifdef USE_CPP11
  ///
  /// higher-order functional
  /// This is like map in haskell, python, etc.
  /// Sample usage:
  ///   vector<int> a = {1, 2, 3, 4, 5};
  ///   vector<int> b = myLibrary::_Map<int, int>(a, [](int n){
  ///     return n * n;
  ///   });
  /// Result:
  ///   b = 1, 4, 9, 16, 25
  ///
  template<typename T_IN, typename T_OUT, class Functor>
  vector<T_OUT> _Map(vector<T_IN> src, Functor func) {
    vector<T_OUT> ret;
    for (int i = 0; i < src.size(); i++) {
      ret.push_back(func(src[i]));
    }
    return ret;
  }
#endif
};

struct State {
public:
  bool onGrand;
  bool isLeftUp;
  bool isRightUp;
  
  State(): onGrand(true), isLeftUp(false), isRightUp(false) { }
};

enum Square {
  BLACK, RED
};

struct Position {
public:
  int x, y;
  Position() { };
  Position(int x, int y): x(x), y(y) { };
};

int main() {
  while (true) {
    int W = Scanner::nextInt();
    int H = Scanner::nextInt();
    if (W + H == 0) break;
    
    Square field[21][21];
    memset(field, RED, sizeof(field));
    
    Position startPos;    
    REP(i, H) {
      string input = Scanner::nextString();
      REP(j, W) {
        switch (input[j]) {
          case '.': { field[i][j] = BLACK;  break; }
          case '#': { field[i][j] = RED;    break; }
          case '@': { 
            startPos.x = i;
            startPos.y = j;
            field[i][j] = RED; 
            break; 
          }
        }
      }  
    }
    
    int count = 1;
    
    queue<Position> q;
    q.push(startPos);
     
    int dx[4] = { 0, -1, 1, 0 };
    int dy[4] = { -1, 0, 0, 1 };
    
    while (!q.empty()) {
      Position p = q.front(); q.pop();
      REP(i, 4) {
        int nx = p.x + dx[i];
        int ny = p.y + dy[i];
        if (nx < 0) continue;
        if (ny < 0) continue;
        
        if (field[nx][ny] == BLACK) {
          q.push(Position(nx, ny));
          field[nx][ny] = RED;
          count++;
        } 
      }  
    } 
    PRINT(count);
  }
  return 0;
}