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())
	}
}

Python: def f(h,w):
  global W,H,S,A
  if h<0 or h>=H or w<0 or w>=W or S[h][w]=="#" or A[h][w]==1:
    return
  A[h][w] = 1
  f(h-1,w)
  f(h+1,w)
  f(h,w-1)
  f(h,w+1)
while True:
  W,H = map(int,input().split())
  if W+H == 0:
    break
  S = [list(input()) for h in range(H)]
  A = [[0 for w in range(W)] for h in range(H)]
  for h in range(H):
    for w in range(W):
      if S[h][w] == "@":
        f(h,w)
        break
  ans = 0
  for i in A:
    ans += sum(i)
  print(ans)

Python: # -*- coding: utf-8 -*-
#rea and blac
h,w=1,1

count=0

def search(x,y):
    #マップの外側か壁の場合は何もしない
    #print(x,y)
    global count
    if x<0 or x>w-1 or y<0 or y>h-1 or map_data[y][x]=='#':
 
        return
        
    
    #以前に到達していたら何もしない
    if reached[y][x]:
         return

    reached[y][x]=1
    count+=1
    #print("aa")



    search(x+1,y)#右
    search(x-1,y)#左
    search(x,y+1)#上
    search(x,y-1)#下
    



while h!=0 and w!=0: 

    count=0
    #グラフの入力方法------

    w,h=map(int ,raw_input().split())
    if h==0 and w==0:
        break

    map_data = [[0]*w for _ in range(h)]
    reached = [[0]*w for _ in range(h)]
    for i in range(h):
        ct = raw_input()
        #print(len(ct))
        for j in range(w):
            map_data[i][j] = ct[j]
            if ct[j]=="@":
                sx=j
                sy=i

    #------



    search(sx,sy)

    print(count)
    count=0
    w=1
    h=1

Python: h=0
w=0

while 1:
    w,h=map(int,input().split())
    if h==0 and w==0:
        break
    grid=[]
    sx=-1
    sy=-1
    ans=1
    used=[[0]*w for i in range(h)]
    def valid(i,j):
        return i>=0 and j>=0 and i<h and j<w and grid[i][j]=='.' and not used[i][j]
    for i in range(h):
        row=input()
        grid.append(row)
        for j in range(w):
            if row[j]=='@':
                sx=i
                sy=j
    stk=[(sx,sy)]
    while stk:
        x=stk[-1][0]
        y=stk[-1][1]
        stk.pop()
        for d in [(1,0),(0,1),(-1,0),(0,-1)]:
            xx=x+d[0]
            yy=y+d[1]
            if valid(xx,yy):
                stk.append((xx,yy))
                used[xx][yy]=1
                ans+=1
    print(ans)

Python: #!/usr/bin/env python
# conding: utf

from logging import getLogger, StreamHandler, NullHandler, DEBUG, INFO
logger = getLogger(__name__)
#handler = StreamHandler()
handler = NullHandler()
logger.setLevel(DEBUG)
handler.setLevel(DEBUG)
logger.addHandler(handler)
logger.propagate = False

g_field = []
g_count = 0
g_W = -1
g_H = -1

OFFSETS = [(1,0), (-1,0), (0,1), (0,-1)]

def dfs(x, y):
    global g_field
    global g_count
    global g_W
    global g_H


    g_count += 1

    g_field[y][x] = "-"

    for dx, dy in OFFSETS:
        logger.debug("diff: {} {}".format(dx, dy))
        new_x = x + dx
        new_y = y + dy

        if new_x < 0 or new_x >= g_W:
            continue
        if new_y < 0 or new_y >= g_H:
            continue
        new_tile = g_field[new_y][new_x]
        if new_tile == "#" or new_tile == "-":
            continue

        logger.debug("{}, {}".format(new_x, new_y))
        dfs(new_x, new_y)


if __name__ == "__main__":
    while True:
        g_W, g_H = [int(s) for s in input().strip().split()]

        if g_W == 0 and g_H == 0:
            break
        
        g_field = []
        for _ in range(g_H):
            row = list(input().strip())
            g_field.append(row)
        g_count = 0

        for y in range(g_H):
            for x in range(g_W):
                if g_field[y][x] == "@":
                    start_x = x
                    start_y = y
                    break

        dfs(start_x, start_y)

        print(g_count)

Python: from collections import deque
while True:
    W,H = map(int,input().split())
    if W == 0: break
    src = [input() for i in range(H)]
    for y,row in enumerate(src):
        x = row.find('@')
        if x < 0: continue
        sx,sy = x,y
        break
    visited = [[0 for x in range(W)] for y in range(H)]
    visited[sy][sx] = 1
    q = deque([(sx,sy)])
    ans = 1
    while q:
        x,y = q.popleft()
        for dx,dy in zip([1,0,-1,0],[0,1,0,-1]):
            nx,ny = x+dx,y+dy
            if not(0 <= nx < W) or not(0 <= ny < H): continue
            if src[ny][nx] == '#' or visited[ny][nx]: continue
            visited[ny][nx] = 1
            ans += 1
            q.append((nx,ny))
    print(ans)