#include<cstdio>

#include<cstring>

#include<queue>

#include<vector>

#include<algorithm>

using namespace std;

const int maxn=800004;

const int INF=10000000;

int A[205][205],B[205][205];

int dy[]={-1,-2,-2,-1,1,2,2,1};

int dx[]={-2,-1,1,2,-2,-1,1,2};

# define  pb push_back

int s,t;

struct Edge{

	int from,to,cap;

	Edge(int u,int v,int c):from(u),to(v),cap(c) {}

};

struct Dicnic{

   vector<Edge>edges;

   vector<int>G[maxn];

   int d[maxn],vis[maxn],cur[maxn];

   queue<int>Q;

   void addedge(int u,int v,int c){

	edges.pb(Edge(u,v,c));               //正向弧

	edges.pb(Edge(v,u,0));               //反向弧

	int m=edges.size();

	G[u].pb(m-2);

	G[v].pb(m-1);

   }

   int BFS()

   {

	memset(vis,0,sizeof(vis));

	d[s]=0,vis[s]=1;Q.push(s);

	while(!Q.empty()){

		int u=Q.front();Q.pop();

		int sz=G[u].size();

		for(int i=0;i<sz;++i){

			Edge e=edges[G[u][i]];

			if(!vis[e.to]&&e.cap>0){

				d[e.to]=d[u]+1,vis[e.to]=1;

				Q.push(e.to);

			}

		}

	}

	return vis[t];

   }

   int dfs(int x,int a){

	   if(x==t)return a;

	   int sz=G[x].size();

	   int f,flow=0;

	   for(int i=cur[x];i<sz;++i){

		Edge e=edges[G[x][i]];

		cur[x]=i;

		if(d[e.to]==d[x]+1&&e.cap>0){

			f=dfs(e.to,min(a,e.cap));

			if(f)

			{

				int u=G[x][i];

				a-=f;

				edges[u].cap-=f;

				edges[u^1].cap+=f;

				flow+=f;

				if(a==0)break;

			}

		}

	   }

	   return flow;

   }

   int maxflow(){

	int ans=0;

	while(BFS()){

	  memset(cur,0,sizeof(cur));

	  ans+=dfs(s,INF);

	}

	return ans;

   }

}op;

int main()

{

	int n,m;

	scanf("%d%d",&n,&m);

	int cnt=0;

	s=0;

	for(int i=1;i<=n;++i)

		for(int j=1;j<=n;++j){

                                     A[i][j]=++cnt;

		}

	t=cnt*2+1;

	for(int i=1;i<=m;++i)

	{

		int a,b;

		scanf("%d%d",&a,&b);

		B[a][b]=1;

	}

	for(int i=1;i<=n;++i)

	{

		for(int j=1;j<=n;++j)

		{

			if(B[i][j])continue;

                                     for(int ii=0;ii<8;++ii)

                                     {

                                              int yy=dy[ii]+i,xx=dx[ii]+j;

                                                      if(yy>=1&&yy<=n&&xx>=1&&xx<=n)

                                                      	 if(!B[yy][xx])op.addedge(A[i][j],A[yy][xx]+cnt,INF);

                                     }

		}

	}

	for(int i=1;i<=n;++i)

	        for(int j=1;j<=n;++j)

	        {

	    	if(!B[i][j])op.addedge(s,A[i][j],1);

	    }

	for(int i=cnt+1;i<=cnt+cnt;++i)

	{

		op.addedge(i,t,1);

	}

	int ans=cnt-op.maxflow()/2;

	printf("%d\n",ans-m);

	return 0;

}