// #Sazaの1日1AC
#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000000 + 7;
const long long INF = 9e18;
const double PI = 3.14159265358979323846;

//マクロ
//型エイリアス
using ll = long long;
using P = pair<long long, long long>;
using vl = vector<long long>;
using vvl = vector<vector<long long>>;
using vP = vector<pair<long long, long long>>;
//ショートカット
#define rep(i, n) for (int i = 0; i < n; i++)
#define rep2(i, k, n) for (int i = k; i < n; i++) //半開区間
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define pb push_back
#define mkp make_pair
//入力
#define vin(v, N) for (long long i = 0; i < N; i++) cin >> v.at(i)
#define lin(n)long long n;cin >> n
#define chin(x)char x;cin >> x;
#define sin(s)string s;cin >> s;
#define vlin(v, N)vector<long long> v(N);for (long long i = 0; i < N; i++)cin >> v.at(i)
#define max(a, b) max((ll)a, (ll)b)
#define min(a, b) min((ll)a, (ll)b)

//関数
//最大公約数
long long gcd(long long m, long long n){
  long long a = max(m, n);
  long long b = min(m, n);
  long long r = a % b;
  while (r != 0){
    a = b;
    b = r;
    r = a % b;
  }
  return b;
}
// 最小公倍数
long long lcd(long long m, long long n){
  return m * n / gcd(m, n);
}
//xのn乗
long long power(long long x, long long N){
  long long ret = 1;
  for (long long i = 0; i < N; i++)
    ret *= x;
  return ret;
}
//繰り返し二乗法
long long repeat_squaring(long long x, long long n){
  if (n == 0)
    return 1;
  else if (n % 2 == 0)
  {
    long long t = repeat_squaring(x, n / 2);
    return t * t % mod;
  }
  else
    return x * repeat_squaring(x, n - 1);
}
//素因数分解(mapで返す)
map<long long, long long> factor(long long p){
  ll p1 = p;
  map<long long, long long> ret;
  for (long long i = 2; i * i <= p1; i++)
  {
    while (p % i == 0)
    {
      ret[i]++;
      p /= i;
    }
  }
  if (p != 1)
    ret[p]++;
  return ret;
}
//素数判定
bool is_prime(long long N){
  for (long long i = 2; i * i <= N; i++)
  {
    if (N % i == 0)
      return false;
  }
  return true;
}
//最大値更新
void chmax(long long &a, long long b){
  a = max(a, b);
}
//最小値更新
void chmin(long long &a, long long b){
  a = min(a, b);
}

//構造体
//Union-Find木
struct UnionFind
{
  //メンバ変数
  vector<long long> par; //par[i]:=頂点iの親
  vector<long long> s;   //s[i]:=頂点iが属する集合の個数(iが根のとき)

  //コンストラクタ
  UnionFind(long long N) : par(N), s(N){
    for (long long i = 0; i < N; i++)
    {
      par[i] = i; //最初はすべてが根として初期化
      s[i] = 1;
    }
  }
  //メンバ関数
  //root(i):=頂点iの根
  long long root(long long i){
    if (par[i] == i)
      return i;
    par[i] = root(par[i]); //経路圧縮
    return root(par[i]);   //再帰
  }
  //size[i]:=iが属する集合の個数
  long long size(long long i){
    return s[root(i)];
  }
  //same(x,y) xとyが同じ根を持つか(同じ集合に含まれるか)
  bool same(long long x, long long y){
    return root(x) == root(y);
  }
  //unite(x,y) xの根をyの根に繋げる(集合を合併)
  void unite(long long x, long long y){
    if (!same(x, y)){
      long long rx = root(x);
      long long ry = root(y);
      par[rx] = par[ry];
      s[ry] = s[rx] + s[ry];
    }
  }
};
//Binary Indexed Tree
struct BIT{
  vector<long long> bit;
  long long N;

  BIT(long long n){
    N = n;
    bit.resize(N + 1);
  }

  void add(long long i, long long w){
    for (long long x = i; x <= N; x += x & -x){
      bit[x] += w;
    }
  }
  long long sum(long long i){
    long long ret = 0;
    for (long long x = i; x > 0; x -= x & -x){
      ret += bit[x];
    }
    return ret;
  }
};
/////////////////⊂('ω'⊂ )))Σ≡GO!/////////////////



ll dh[] = {1,-1,0,0};
ll dw[] = {0,0,1,-1};

int main(){
  //doubleの桁数
  cout << fixed << setprecision(10);

  while(true){
    lin(W);lin(H);
    if(H == 0) break;
    vvl ver(H,vl(W-1));
    vvl hor(H-1,vl(W));
    rep(h,2*H-1){
      if(h%2 == 0){
        rep(w,W-1) cin >> ver.at(h/2).at(w);
      }
      else{
        rep(w,W) cin >> hor.at(h/2).at(w);
      }
    }
  
    vvl d(H,vl(W,-1));
    d[0][0] = 1;
    queue<P> Q;
    Q.push(mkp(0,0));
    while(Q.size() > 0){
      ll h = Q.front().first, w = Q.front().second; Q.pop();
      rep(i,4){
        ll nh = h + dh[i], nw = w + dw[i];
        if(0 <= nh && nh < H && 0 <= nw && nw < W && d[nh][nw] == -1){
          if(i == 0 && hor.at(h).at(w) == 0 || i == 1 && hor.at(h-1).at(w) == 0 || i == 2 && ver.at(h).at(w) == 0 || i == 3 && ver.at(h).at(w-1) == 0){
            d[nh][nw] = d[h][w] + 1;
            Q.push(mkp(nh,nw));
          }

        }
      }
    }
    cout << max(d[H-1][W-1], 0) << endl;
  }

}

  


Measured memory_bytes: 3064