Problem: Taro loves chocolate and when he returns from school he eats his favorite chocolate bar with a heart symbol on it. A recent pleasure is to eat all the heart symbol blocks to the end. Taro , Try to eat as many heartless blocks as possible, with all heartmark blocks connected.

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However, Taro is still young, and even if he tries to eat as above, useless blocks will remain. Therefore, Taro seeks the maximum number of blocks that can be eaten when all the heart-shaped blocks are left connected. I asked you to create a program.

Taro can eat whatever way he wants, as long as all the heart-shaped blocks are connected. If one side of one block does not touch the other block, it will be separated.



Input

The input consists of multiple datasets, each dataset given in the following format:


H W
H x W numbers


H and W are integers indicating the vertical size and horizontal size of the chocolate bar, respectively. H x W numbers represent block information, '0' representing blocks without a heart mark, and blocks with a heart mark. Consists of '1'.

The end of the input is indicated by the dataset where H = W = 0. Do not output for this case.

You can assume that 1 ≤ H, W ≤ 12 and the number of heart-shaped blocks is 6 or less.

Output

For each dataset, output the maximum number of blocks that Taro can eat.

Example

Input

4 4
1 0 0 0
0 0 1 0
0 1 0 0
1 0 0 1
1 1
1
2 3
1 0 0
0 0 1
0 0


Output

7
0
2

Solution (in CPP):

Solution:
#include <iostream>
#include <cstdio>
#include <vector>
#include <list>
#include <complex>
#include <algorithm>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <cstring>
#include <stack>
#include <cmath>
#include <iomanip>
#include <sstream>
#include <fstream>
#include <cassert>
#include <numeric>
using namespace std;
typedef long long ll;
typedef pair<int,int> PI;
#define EPS (1e-10)
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define REP(i, n) rep (i, n)
#define F first
#define S second
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define min3(a,b,c) min((a),min((b),(c)))
#define min4(a,b,c,d) min((a),min3((b),(c),(d)))
#define SZ(a) (int)((a).size())
#define ALL(a) a.begin(),a.end()
#define FLL(a,b) memset((a),b,sizeof(a))
#define CLR(a) memset((a),0,sizeof(a))
#define FOR(it,a) for(__typeof(a.begin())it=a.begin();it!=a.end();++it)
template<typename T,typename U> ostream& operator<< (ostream& out, const pair<T,U>& val){return out << "(" << val.F << ", " << val.S << ")";}
template<class T> ostream& operator<< (ostream& out, const vector<T>& val){out << "{";rep(i,SZ(val)) out << (i?", ":"") << val[i];return out << "}";}
typedef double FP;
typedef complex<FP> pt;
typedef pt P;
typedef pair<pt,pt> line;
FP dot(P a,P b){return real(conj(a)*b);}
FP crs(P a,P b){return imag(conj(a)*b);}
P ortho(P a){return a*P(0,1);}
P ortho(line a){return ortho(a.S-a.F);}
P crspt(P a,P b,P c,P d){b-=a,d-=c;return a+b*crs(d,c-a)/crs(d,b);}
P crspt(line a,line b){return crspt(a.F,a.S,b.F,b.S);}
bool onl(P a1,P a2,P b){return abs(b-a1)+abs(b-a2)<abs(a1-a2)+EPS;}
bool onl(line a,P b){return onl(a.F,a.S,b);}
bool iscrs(line a,line b){P c=crspt(a,b);return onl(a,c)&&onl(b,c);}
void pkuassert(bool t){t=1/t;};
int dx[]={0,1,0,-1,1,1,-1,-1};
int dy[]={1,0,-1,0,-1,1,1,-1};
enum{TOP,BTM,LFT,RGT,FRT,BCK};
int dxdy2ce[]={RGT,FRT,LFT,BCK};
template<class T> T shift(T a,int b,int c,int d,int e){
 __typeof(a[0])t=a[b];a[b]=a[c];a[c]=a[d];a[d]=a[e];a[e]=t;
 return a;}
template<class T> T rgt(T a){return shift(a,TOP,LFT,BTM,RGT);}
template<class T> T lft(T a){return shift(a,TOP,RGT,BTM,LFT);}
template<class T> T frt(T a){return shift(a,TOP,BCK,BTM,FRT);}
template<class T> T bck(T a){return shift(a,TOP,FRT,BTM,BCK);}
line mkl(P a,P v){return line(a,a+v);}
FP lpdist(line a,P b){return abs(b-crspt(a,mkl(b,ortho(a))));}
FP spdist(line a,P b){
  P c(crspt(a,mkl(b,ortho(a))));
  return onl(a,c)?abs(b-c):min(abs(a.F-b),abs(a.S-b));
}
FP ssdist(line a,line b){
 return
  iscrs(a,b)?0.:
   min4(spdist(a,b.F),spdist(a,b.S),
        spdist(b,a.F),spdist(b,a.S));
}
namespace std{
  bool operator<(const P&a,const P&b){
    return mp(real(a),imag(a))<mp(real(b),imag(b));
  }
}

int h,w;
int in[12][12];

PI rinsetu[12*12];
int rsz;
bool isrinsetu[12][12];
bool issh[12][12];
vector<PI> choco;
PI tree[12*12];
int tsz=0;
int row[12],col[12];

int maxdist[6];

bool iddfs(int depth,int ne,int ch){
  if(depth==0)
    return ch==SZ(choco);

  if(ne)
    rep(j,SZ(choco))
      if(depth<maxdist[j]) return false;
  if(ne&&ch==SZ(choco)-1) return true;
  
  int crsz=rsz;
  int back[6];
  rep(i,SZ(choco)) back[i]=maxdist[i];
  
  for(int i=ne;i<crsz;++i){
    PI node=rinsetu[i];
    if(!row[node.F] && !col[node.S]) continue;
    bool flag[4]={};
    int nu=0;
    rep(k,4){
      int nx=node.F+dx[k];
      int ny=node.S+dy[k];
      if(min(nx,ny)<0 || nx>=h || ny>=w) continue;
      nu += issh[nx][ny];
      if(isrinsetu[nx][ny])
        continue;
      isrinsetu[nx][ny]=true;
      flag[k]=true;
      rinsetu[rsz++]=PI(nx,ny);
    }
    issh[node.F][node.S]=true;
    tree[tsz++]=node;
    int ok=0;
    //bool ok=false;
    rep(j,SZ(choco)){
      int b=maxdist[j];
      maxdist[j]=
      min(maxdist[j],
          abs(node.F-choco[j].F)+abs(node.S-choco[j].S));
      ok|=(b!=maxdist[j])<<j;
    }
    
    if((nu<2 || in[node.F][node.S]) && ok &&
       iddfs(depth-1,i+1,ch+in[node.F][node.S]))
      return true;
    
    rep(j,SZ(choco)) maxdist[j]=back[j];
    
    --tsz;
    rep(k,4)if(flag[k]){
      int nx=node.F+dx[k];
      int ny=node.S+dy[k];
      isrinsetu[nx][ny]=false;
    }
    rsz=crsz;
    issh[node.F][node.S]=false;
    if(in[node.F][node.S]) return false;
  }
  return false;
}



void solve(){
  CLR(row);
  CLR(col);
  int low=0;
  choco.clear();
  rep(i,h)rep(j,w){
    cin >> in[i][j];
    low += in[i][j];
    row[i]+=in[i][j];
    col[j]+=in[i][j];
    if(in[i][j]) choco.pb(mp(i,j));
  }
  

  if(SZ(choco)<1){
    cout << h*w << endl;
    return;
  }
  int maxdist=0;
  rep(i,SZ(choco))rep(j,i)
    maxdist=
    max(maxdist,
        abs(choco[i].F-choco[j].F)+abs(choco[i].S-choco[j].S));
  low=max(low,maxdist);
  
  for(int depth=low;depth<=h*w;++depth){
    //cerr << depth << endl;
    CLR(isrinsetu);
    CLR(issh);
    rsz=0;
    int idx=0;rand()%SZ(choco);
    rinsetu[rsz++]=choco[idx];
    //cerr << choco[idx] << endl;
    isrinsetu[choco[idx].F][choco[idx].S]=1;
    tsz=0;
    rep(i,SZ(choco)) ::maxdist[i]=140;
    
    if(iddfs(depth,0,0)){
      cout << h*w-depth << endl;
      return;
    }
  }
  
}

int main(int argc, char *argv[])
{
  while(cin >> h >> w && h) solve();
}