Go: package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	io := NewIo()
	defer io.Flush()
	for {
		w, h := io.NextInt(), io.NextInt()
		if w == 0 {
			break
		}
		xWall := make([][]int, h)
		yWall := make([][]int, h)
		for i := 0; i < h; i++ {
			xWall[i], yWall[i] = make([]int, w), make([]int, w)
			for j := 0; j < w; j++ {
				xWall[i][j], yWall[i][j] = -1, -1
			}
		}
		for i := 0; i < h*2-1; i++ {
			if i%2 == 0 {
				for j := 0; j < w-1; j++ {
					xWall[i/2][j] = io.NextInt()
				}
			} else {
				for j := 0; j < w; j++ {
					yWall[i/2][j] = io.NextInt()
				}
			}
		}
		//io.Println(bfs(w, h, xWall, yWall))
		fmt.Println(bfs(w, h, xWall, yWall))
	}
}

type P struct {
	x, y int
}

func bfs(w, h int, x, y [][]int) int {
	d := make([][]int, h)
	for i := 0; i < h; i++ {
		d[i] = make([]int, w)
	}
	q := list.New()
	q.PushBack(P{0, 0})
	d[0][0] = 1

	for q.Len() != 0 {
		pos := q.Remove(q.Front()).(P)
		if pos.x == w-1 && pos.y == h-1 {
			break
		}
		if pos.x > 0 && x[pos.y][pos.x-1] == 0 && d[pos.y][pos.x-1] == 0 {
			d[pos.y][pos.x-1] = d[pos.y][pos.x] + 1
			q.PushBack(P{pos.x - 1, pos.y})
		}
		if pos.x < w-1 && x[pos.y][pos.x] == 0 && d[pos.y][pos.x+1] == 0 {
			d[pos.y][pos.x+1] = d[pos.y][pos.x] + 1
			q.PushBack(P{pos.x + 1, pos.y})
		}
		if pos.y > 0 && y[pos.y-1][pos.x] == 0 && d[pos.y-1][pos.x] == 0 {
			d[pos.y-1][pos.x] = d[pos.y][pos.x] + 1
			q.PushBack(P{pos.x, pos.y - 1})
		}
		if pos.y < h-1 && y[pos.y][pos.x] == 0 && d[pos.y+1][pos.x] == 0 {
			d[pos.y+1][pos.x] = d[pos.y][pos.x] + 1
			q.PushBack(P{pos.x, pos.y + 1})
		}
	}
	return d[h-1][w-1]
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

Python: from collections import deque

def solve(W, H, walls):
    edge = [[[] for i in range(W)] for j in range(H)]
    for i in range(H):
        for j in range(W-1):
            if (not walls[2*i][j]):
                edge[i][j].append((i, j+1))
                edge[i][j+1].append((i,j))
    for i in range(H-1):
        for j in range(W):
            if (not walls[2*i+1][j]):
                edge[i][j].append((i+1, j))
                edge[i+1][j].append((i,j))

    q = deque()
    q.append((0, 0))
    dist = [[-1]*W for i in range(H)]
    dist[0][0] = 1

    while q:
        y, x = q.popleft()
        for ny, nx in edge[y][x]:
            if (dist[ny][nx] == -1):
                dist[ny][nx] = dist[y][x] + 1
                q.append((ny, nx))


    return dist[H-1][W-1] if (dist[H-1][W-1] != -1) else 0

"""
def solve(W, H, walls):
    dire = [(1,0), (0,1), (-1,0), (0,-1)]
    field = [[1]*(2*W) for i in range(2*H)]
    for i in range(0,2*H,2):
        vertical_wall = walls[i]
        for j in range(W-1):
            if (vertical_wall[j]):
                field[i][j*2+1] = field[i+1][j*2+1] = 0

    for i in range(1,2*H-1,2):
        horizontal_wall = walls[i]
        for j in range(W):
            if (horizontal_wall[j]):
                field[i][j*2] = field[i][j*2+1] = 0

    q = deque()
    dist = [[-1]*(2*W) for i in range(2*H)]
    q.append((0,0))
    dist[0][0] = 0

    while q:
        y, x = q.popleft()
        for dy, dx in dire:
            if (y+dy<2*H) and (y+dy>=0) and (x+dx<2*W) and (x+dx>=0):
                if (field[y+dy][x+dx]) and (dist[y+dy][x+dx] == -1):
                    dist[y+dy][x+dx] = dist[y][x] + 1
                    q.append((y+dy, x+dx))
    res = dist[2*H-1][2*W-1]//2

    for i in field:
        for j in i:
            print("." if j else "#", end="")
        print()

    ans_dist = [[0]*W for i in range(H)]
    for i in range(H):
        for j in range(W):
            ans_dist[i][j] = max(dist[2*i][2*j], dist[2*i][2*j+1], dist[2*i+1][2*j], dist[2*i+1][2*j+1]) // 2
    for i in ans_dist:
        print(i)

    #for i in dist:
       # print(i)

    return res if (res != -1) else 0

"""
def main():
    ans = []
    while True:
        W, H = map(int, input().split())
        if (W==0) and (H==0):
            break
        walls = [list(map(int, input().split())) for i in range(2*H-1)]
        ans.append(solve(W, H, walls))
    
    for i in ans:
        print(i)

main()

Python: from collections import deque

ans = []
while True:
  w,h = map(int,input().split())
  if w==h==0: 
    # for a in ans:
    #   print(a)
    exit()

  maze = []
  for k in range(h):
    # [(lower, right)]
    row = [ [0,0] for _ in range(w) ]
    
    for i in range(2):
      if i==0:
        # check for right boundary
        v = list(map(int,input().split()))
        for j in range(w-1):
          if v[j] == 1:
            row[j][1] = 1
      else:
        # check for lower boundary
        if k == h-1: continue
        v = list(map(int,input().split()))
        for j in range(w):
          if v[j] == 1:
            row[j][0] = 1

    maze.append(row)

  dist = [ [-1]*w for _ in range(h) ]
  dist[0][0] = 1
  q = deque([(0,0)])

  while q:
    r,c = q.popleft()

    directions = []

    # lower
    if maze[r][c][0] == 0:
      directions.append((1,0))

    # right
    if maze[r][c][1] == 0:
      directions.append((0,1))

    # upper
    if r-1>=0 and maze[r-1][c][0] == 0:
      directions.append((-1,0))

    # left
    if c-1>=0 and maze[r][c-1][1] == 0:
      directions.append((0,-1))


    for x,y in directions:
      nr,nc = r+x,c+y
      # import pdb; pdb.set_trace()
      if 0 <= nr < h and 0 <= nc < w:
        if dist[nr][nc] != -1: continue
        if (nr,nc) in q: continue
        dist[nr][nc] = dist[r][c] + 1
        if nr == h-1 and nc == w-1:
          break
        else:
          q.append((nr,nc))

  if dist[h-1][w-1] == -1:
    ans.append(0)
    print(0)
  else:
    ans.append(dist[h-1][w-1])
    print(dist[h-1][w-1])


for a in ans:
  print(a)