#include<iostream>

#include<cstdio>

#include<cstring>

using namespace std;

const int MAXN = *;

//const int MAXM = 205*205;

const int MAXM = *MAXN;

inline int rd(){

    int x=,f=;char ch=getchar();

    while(!isdigit(ch)) {f=ch=='-'?:;ch=getchar();}

    while(isdigit(ch))  {x=(x<<)+(x<<)+ch-'';ch=getchar();}

    return f?x:-x;

}

int xx[]={,,-,-,-,-,,},yy[]={,,,,-,-,-,-};

int n,m,head[MAXN],cnt,vis[MAXN],match[MAXN];

int to[MAXM<<],nxt[MAXM<<],num,ans;

bool ban[][];

inline void add(int bg,int ed){

//    cout<<bg<<" "<<ed<<endl;

    to[++cnt]=ed,nxt[cnt]=head[bg],head[bg]=cnt;

}

inline void bfs(int x,int y){

    for(register int i=;i<=;i++){

        int ii=xx[i]+x,jj=yy[i]+y;

        if(ii< || ii>n || jj< || jj>n || ban[ii][jj]) continue;

        add((x-)*n+y,(ii-)*n+jj);

    }

}

bool dfs(int x){

    for(register int i=head[x];i;i=nxt[i]){

        int u=to[i];if(vis[u]==num) continue;

        vis[u]=num;

        if(!match[u] || dfs(match[u])) {match[u]=x;return true;}

    }

    return false;

}

int main(){

    n=rd(),m=rd();int x,y;

    for(register int i=;i<=m;i++){

        x=rd(),y=rd();

        ban[x][y]=;

    }

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

        for(register int j=(+((i-)&));j<=n;j+=)

            if(!ban[i][j]) bfs(i,j);

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

        for(register int j=(+((i-)&));j<=n;j+=)

            if(!ban[i][j]) num++,ans+=dfs((i-)*n+j);

    cout<<(n*n-m)-ans;

    return ;

}