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: anslist = []
def sarch(i, j, visited):

    if 0 < i:
        if visited[i - 1][j] == 0:
            visited[i - 1][j] = 1
            sarch(i - 1, j, visited)
    if i < len(visited) - 1:
        if visited[i + 1][j] == 0:
            visited[i + 1][j] = 1
            sarch(i + 1, j, visited)
    if 0 < j:
        if visited[i][j - 1] == 0:
            visited[i][j - 1] = 1
            sarch(i, j - 1, visited)
    if j < len(visited[0]) - 1:
        if visited[i][j + 1] == 0:
            visited[i][j + 1] = 1
            sarch(i, j + 1, visited)
    return visited


while True:
    w, h = map(int, input().split())
    if w == 0 and h == 0:
        break
    grid = [list(input()) for i in range(h)]
    visited = [[0 for i in range(w)] for j in range(h)]
    starti = 0
    startj = 0
    for i in range(h):
        for j in range(w):
            if grid[i][j] == "@":
                starti = i
                startj = j
                visited[i][j] = 1
            elif grid[i][j] == "#":
                visited[i][j] = -1
            else:
                visited[i][j] = 0

    visited = sarch(starti, startj, visited)
    #print(visited)
    ans = 0
    for i in visited:
        for j in i:
            if j == 1:
                ans += 1
    anslist.append(ans)

for i in anslist:
    print(i)

Python: #data????§???????[y???][x???]??§??????

if __name__ == "__main__":
    while 1:
        w,h = list(map(int,input().strip().split()))
        if w == h == 0:break
        data = []
        data = []
        for _ in range(h):data.append(list(input()))
        visited = []
        position =(0,0)
        for i in range(h):
            if '@'in data[i]:position = (i,data[i].index('@'))
        stack = []
        count = 0
        stack.append(position)
        while len(stack) !=0:
            y,x= stack.pop()
            count +=1
            if y-1 >= 0 and not (y-1,x)in visited and data[y -1][x] == '.':
                visited.append((y-1,x))
                stack.append((y-1,x))
            if x -1 >= 0 and not (y,x-1)in visited and data[y][x-1] == '.':
                visited.append((y,x-1))
                stack.append((y,x-1))
            if y +1 < h and not (y+1,x)in visited and data[y +1][x] == '.':
                visited.append((y+1,x))
                stack.append((y+1,x))
            if x + 1 < w and not (y,x+1)in visited and data[y][x +1] == '.':
                visited.append((y,x+1))
                stack.append((y,x+1))

        print(count)

Python: data, res

def valid(x, y):
    global data
    return 0 <= x < W and 0 <= y < H and data[y][x] != '#'

def dfs(x, y):
    global data, res
    if valid(x, y):
        res += 1
        data[y][x] = '#'
        dx = [1, 0, -1, 0]
        dy = [0, 1, 0, -1]
        for i in range(4):
            dfs(x + dx[i], y + dy[i])
    else:
        return
    
while True:
    global data, res
    W, H = map(int, input().split())
    if not W:
        break
    data = [list(input()) for _ in range(H)]
    res = 0
    for i in range(W):
        for j in range(H):
            if data[j][i] == '@':
                dfs(i, j)
                break
    print(res)

Python: import copy
w, h = map(int,input().split())
while [h, w] != [0, 0]:
    area = []
    a = 1
    for i in range(h):
        area.append(list(input()))
        area[i].insert(0,"#")
        area[i].append("#")
    area.insert(0,["#" for i in range(w + 2)])
    area.append(["#" for i in range(w + 2)])

    que = []
    for i in range(1, h + 1):
        for j in range(1, w + 1):
            if area[i][j] == "@":
                que.append([i, j])
                break
        else:
            continue
        break
    while True:
        nque = []
        for i in que:
            h1 = i[0]
            w1 = i[1]
            if area[h1 - 1][w1] == ".":
                area[h1 - 1][w1] = "*"
                nque.append([h1 - 1, w1])
                a += 1
            if area[h1 + 1][w1] == ".":
                area[h1 + 1][w1] = "*"
                nque.append([h1 + 1, w1])
                a += 1
            if area[h1][w1 - 1] == ".":
                area[h1][w1 - 1] = "*"
                nque.append([h1, w1 - 1])
                a += 1
            if area[h1][w1 + 1] == ".":
                area[h1][w1 + 1] = "*"
                nque.append([h1, w1 + 1])
                a += 1
        if nque == []:
            break
        que = copy.deepcopy(nque)

    print(a)
        
    w, h = map(int,input().split())