#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;
int next[1000001];
int to[1000001];
int val[1000001];
int head[1000001];
int tot=1;
int q[1000001];
int n,k,m;
int S,T;
int ans;
int x,y;
int d[1000001];
int c[1001][1001];
const int dx[]={-2,-1,1,2,2,1,-1,-2};
const int dy[]={1,2,2,1,-1,-2,-2,-1};
void add(int x,int y,int v)
{tot++;next[tot]=head[x];head[x]=tot;to[tot]=y;val[tot]=v;tot++;next[tot]=head[y];head[y]=tot;to[tot]=x;val[tot]=0;
}
bool bfs(int S,int T)
{int r=0;int l=0;memset(q,0,sizeof(q));memset(d,-1,sizeof(d));q[r++]=S;d[S]=0;while(l<r){  int now=q[l];for(int i=head[now];i;i=next[i]){if(d[to[i]]==-1&&val[i]!=0){d[to[i]]=d[now]+1;q[r++]=to[i];}}l++;}if(d[T]==-1){return false;}else{return true;}
}
int dfs(int x,int flow)
{if(x==T){return flow;}int now_flow;int used=0;for(int i=head[x];i;i=next[i]){if(d[to[i]]==d[x]+1&&val[i]!=0){now_flow=dfs(to[i],min(flow-used,val[i]));val[i]-=now_flow;val[i^1]+=now_flow;used+=now_flow;if(now_flow==flow){return flow;}}}if(used==0){d[x]=-1;}return used;
}
void dinic()
{while(bfs(S,T)==true){ans+=dfs(S,0x3f3f3f);}
}
int main()
{scanf("%d%d",&n,&m);S=n*m+16;T=n*m+28;for(int i=1;i<=n;i++){for(int j=1;j<=m;j++){scanf("%d",&c[i][j]);}}for(int i=1;i<=n;i++){for(int j=1;j<=m;j++){if(c[i][j]==0){c[i][j]=(i-1)*m+j;if((i+j)%2==0){add(S,c[i][j],1);}else{add(c[i][j],T,1);}}else{k++;c[i][j]=-1;}}}for(int i=1;i<=n;i++){for(int j=1;j<=m;j++){if(c[i][j]!=-1&&(i+j)%2==0){for(int l=0;l<=7;l++){int fx=dx[l]+i;int fy=dy[l]+j;if(fx>0&&fx<=n&&fy>0&&fy<=m&&c[fx][fy]!=-1){add(c[i][j],c[fx][fy],0x3f3f3f);} }}}}dinic();printf("%d",n*m-k-ans);
}