// includes
#include <bits/stdc++.h>
using namespace std;

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define bit(n) (1LL<<(n))
// functions
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << p.first << " " << p.second; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(20);}
} fast_io_;

template <typename T>
struct Graph {
  int n;
  vector<vector<T> > d;
  vector<vector<int> > path;
  Graph(int n): n(n) {
    d = vector<vector<T>>(n, vector<T>(n, numeric_limits<T>::max() / 10));
    path = vector<vector<int>>(n, vector<int>(n, -1));
    for(int i = 0; i < n; i++)d[i][i] = 0;
  }
  void warshall_floyd(){
    for(int k = 0; k < n; k++){
      for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
          if(d[i][j] > d[i][k] + d[k][j]){
            d[i][j] = d[i][k] + d[k][j];
            path[i][j] = k;
          }
        }
      }
    }
  }
  void adde(int at, int to, T cost){
    d[at][to] = cost;
  }
  vector<T>& operator[](size_t i){
    return d[i];
  }
};

using GraphI = Graph<int>;
using GraphL = Graph<ll>;

template <typename T>
struct SteinerTree{
  int n;
  vector<vector<T>> d;
  T inf = numeric_limits<T>::max() / 10;
  explicit SteinerTree(int n): n(n){
    d.resize(n, vector<T>(n, inf));
    for(int i = 0; i < n; i++)d[i][i] = 0;
  }
  void adde(int from, int to, T cost){
    d[from][to] = min(d[from][to], cost);
  }
  T steiner_tree(const vector<int> &v){
    if(v.size() == 1)return 0;
    // warshall floyd
    Graph<T> g(n);
    for(int i = 0; i < n; i++){
      for(int j = 0; j < n; j++){
        if(i != j && d[i][j] != inf)g.adde(i, j, d[i][j]);
      }
    }
    g.warshall_floyd();

    int t = v.size();
    vector<vector<T>> opt(1 << t, vector<T>(n, inf));
    for(int i = 0; i < t; i++){
      for(int j = 0; j < n; j++){
        opt[1 << i][j] = g.d[v[i]][j];
      }
    }

    for(int s = 0; s < (1 << t); s++){
      if(!(s & (s - 1)))continue;
      for(int p = 0; p < n; p++){
        for(int u = s; ; u = (u - 1) & s){
          opt[s][p] = min(opt[s][p], opt[u][p] + opt[s - u][p]);
          if(u == 0)break;
        }
      }
      for(int p = 0; p < n; p++){
        for(int q = 0; q < n; q++){
          opt[s][p] = min(opt[s][p], opt[s][q] + g.d[p][q]);
        }
      }
    }
    T res = inf;
    for(int s = 0; s < (1 << t); s++){
      for(int p = 0; p < n; p++){
        res = min(res, opt[s][p] + opt[(1<<t)-1-s][p]);
      }
    }
    return res;
  }
};

int c[12][12];

int main(int argc, char const* argv[])
{
  int h, w;
  while(true){
    cin >> h >> w;
    if(h == 0 && w == 0)break;
    SteinerTree<int> st(h * w);
    vector<int> v;
    rep(i, h){
      rep(j, w){
        cin >> c[i][j];
        if(c[i][j] == 1)v.pb(i * w + j);
      }
    }
    rep(i, h){
      rep(j, w){
        rep(k, 4){
          int nx = i + dx[k];
          int ny = j + dy[k];
          if(nx >= 0 && nx < h && ny >= 0 && ny < w){
            st.adde(i * w + j, nx * w + ny, 1);
          }
        }
      }
    }
    int res = h * w - st.steiner_tree(v) - 1;
    cout << res << endl;
  }
  return 0;
}



Measured memory_bytes: 3280