#include<cstdio>
#include<iostream>
using namespace std;
const int dx[]={1,1,2,2,-1,-1,-2,-2};
const int dy[]={2,-2,1,-1,2,-2,1,-1};
const int N=210;
const int M=N*N;
const int inf=0x3f3f3f3f;
int n,m,S,T,num,id[N][N],mp[N][N],head[M],dis[M],q[M*5];
struct node{
    int v,next,cap;
}e[M*10];int tot=1;
void add(int x,int y,int z){
    e[++tot].v=y;e[tot].cap=z;e[tot].next=head[x];head[x]=tot;
    e[++tot].v=x;e[tot].cap=0;e[tot].next=head[y];head[y]=tot;
}
bool bfs(){
    for(int i=S;i<=T;i++) dis[i]=inf;
    int h=0,t=1;
    q[t]=S;dis[S]=0;
    while(h!=t){
        int x=q[++h];
        for(int i=head[x];i;i=e[i].next){
            int v=e[i].v;
            if(e[i].cap&&dis[v]>dis[x]+1){
                dis[v]=dis[x]+1;
                if(v==T) return 1;
                q[++t]=v;
            }
        }
    }
    return dis[T]<inf;
}
int dfs(int x,int f){
    if(x==T) return f;
    int used=0,t;
    for(int i=head[x];i;i=e[i].next){
        int v=e[i].v;
        if(e[i].cap&&dis[v]==dis[x]+1){
            t=dfs(v,min(f,e[i].cap));
            //if(!t) dis[t]=0;//TLE*1
            e[i].cap-=t;e[i^1].cap+=t;
            f-=t;used+=t;
            if(!f) return used;
        }
    }
    dis[x]=0;//TLE*2
    return used;
}
int dinic(){
    int res=0;
    while(bfs()) res+=dfs(S,inf);
    return n*n-m-res;
}
void mapping(){
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            id[i][j]=++num;
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(mp[i][j]) continue;
            if((i+j)&1^1){//黑 
                add(S,id[i][j],1);
                for(int k=0;k<8;k++){
                    int nx=i+dx[k],ny=j+dy[k];
                    if(nx<1||nx>n||ny<1||ny>n||mp[nx][ny]) continue;
                    add(id[i][j],id[nx][ny],1);
                }
            }
            else{//白 
                add(id[i][j],T,1);
            }
        }
    }
}
int main(){
    freopen("knight.in","r",stdin); 
    freopen("knight.out","w",stdout); 
    scanf("%d%d",&n,&m);S=0;T=n*n+1;
    for(int i=1,x,y;i<=m;i++) scanf("%d%d",&x,&y),mp[x][y]=1;
    mapping();
    printf("%d",dinic());
    return 0;
}