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: import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time,copy,functools

sys.setrecursionlimit(10**7)
inf = 10**20
eps = 1.0 / 10**10
mod = 10**9+7

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LI_(): return [int(x)-1 for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def LS(): return sys.stdin.readline().split()
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def S(): return input()
def pf(s): return print(s, flush=True)


def main():
    rr = []

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

    while True:
        w,h = LI()
        if w == 0:
            break
        a = [S() for _ in range(h)]
        q = []
        f = collections.defaultdict(bool)
        for i in range(h):
            for j in range(w):
                if a[i][j] == '@':
                    q.append((i,j))
        qi = 0
        while len(q) > qi:
            i,j = q[qi]
            qi += 1
            for di,dj in dd:
                ni = i + di
                nj = j + dj
                if 0 <= ni < h and 0 <= nj < w and a[ni][nj] == '.' and not f[(ni,nj)]:
                    f[(ni,nj)] = True
                    q.append((ni,nj))
        rr.append(len(q))

    return '\n'.join(map(str, rr))


print(main())

Python: # -*- coding: utf-8 -*-
'''
所要時間は、分位であった。
'''


# ライブラリのインポート
#import re #正規表現
import sys
input = sys.stdin.readline
#import heapq
#import bisect
#import collections
#import math
#from pprint import pprint

def main():
    while 1:
        w, h = map(int, input().split())
        if w == 0 and h == 0: break
        mp = []
        for i in range(h):
            mp.append(list(input().strip()))
            if "@" in mp[-1]:
                stj = mp[-1].index("@")
                sti = i
        flag = [[0]*w for i in range(h)]
        #pprint(flag)
        flag = dfs(sti, stj, flag, mp)
        ans = sum([flag[i].count(1) for i in range(h)])
        print(ans)
        #pprint(flag)
def dfs(rw, cm, flag, mp):
    flag[rw][cm] = 1
    #print(rw,cm)
    #pprint(flag)
    try:
        c = mp[rw][cm-1]
        b = flag[rw][cm-1]
    except: c = "#"
    if c == "." and b == 0 and rw>=0 and cm>0: dfs(rw, cm-1, flag, mp)
    try:
        c = mp[rw-1][cm]
        b = flag[rw-1][cm]
    except: c = "#"
    if c == "." and b == 0 and rw>0 and cm>=0: dfs(rw-1, cm, flag, mp)
    try: 
        c = mp[rw][cm+1]
        b = flag[rw][cm+1]
    except: c = "#"
    if c == "." and b == 0: dfs(rw, cm+1, flag, mp)
    try: 
        c = mp[rw+1][cm]
        b = flag[rw+1][cm]
    except: c = "#"
    if c == "." and b == 0: dfs(rw+1, cm, flag, mp)
    return flag


    


    
if __name__ == '__main__':
    main()

Python: 

def search(a,b,dx,dy,t,check,li,answer):
    for i in range(len(dx)):
            temp = [t[0]+dx[i],t[1]+dy[i]]
            if mapCheck(a,b,temp):
                if check[temp[1]][temp[0]] == 0:
                    if li[temp[1]][temp[0]] == '.':
                        answer += 1
                        check[temp[1]][temp[0]] = 1
                        answer = search(a,b,dx,dy,temp,check,li,answer)
    return answer
                    
                
            
def mapCheck(a,b,t):
    if t[0] <= a-1 and t[0] >=0:
        if t[1] <= b-1 and t[1] >= 0:
            return True
    return False

while True:
    li = []
    answer = 1
    start = [0,0]
    a,b = map(int, input().strip().split(' '))
    dx = [1,0,-1,0]
    dy = [0,1,0,-1]
    if a == 0 and b == 0:
        break
    for i in range(b):
        li.append(input().strip().split())
    check = [[0 for i in range(a)] for j in range(b)]
    for i in range(len(li)):
        li[i] = str(li[i])
        li[i] = list(li[i])
        del li[i][0]
        del li[i][0]
        del li[i][len(li[i])-1]
        del li[i][len(li[i])-1]
        for j in range(len(li[i])):
            if li[i][j] == '@':
                start = [j,i]
    print(search(a,b,dx,dy,start,check,li,answer))

Python: from queue import Queue

while True:
    w, h = map(int, input().split())
    if w == h == 0:
        break

    tile = [input() for i in range(h)]
    for x, col in enumerate(tile):
        if '@' in col:
            y = col.index('@')
            s = (x, y)
            break

    visit = [[False for i in range(w)] for j in range(h)]
    dx = (0, -1, 1, 0)
    dy = (1, 0, 0, -1)
    que = Queue()
    que.put(s)
    while not que.empty():
        x, y = que.get()
        if visit[x][y]:
            continue

        visit[x][y] = True
        for j in range(4):
            sx = x + dx[j]
            sy = y + dy[j]
            if sx < 0 or sx >= h or sy < 0 or sy >= w:
                continue
            if tile[sx][sy] != '#':
                que.put((sx, sy))

    ans = 0
    for col in visit:
        ans += col.count(True)

    print(ans)