#include <cstdio>

#include <cstdlib>

#include <queue>

#include <vector>

#include <cstring>

#include <string>

#include <iostream>

#include <algorithm>

#define inf 0x3f3f3f3f

using namespace std;

const int INF = 0x3f3f3f3f;

const int maxn = 1e5 + ;

struct edge

{

    int u, v, c, f;

    edge(int u, int v, int c, int f) :u(u), v(v), c(c), f(f) {}

};

vector<edge>e;

vector<int>G[maxn];

int level[maxn];//BFS分层，表示每个点的层数

int iter[maxn];//当前弧优化

int m;

void init(int n)

{

    for (int i = ; i <= n; i++)G[i].clear();

    e.clear();

}

void add(int u, int v, int c)

{

    e.push_back(edge(u, v, c, ));

    e.push_back(edge(v, u, , ));

    m = e.size();

    G[u].push_back(m - );

    G[v].push_back(m - );

    //printf("ww %d %d %d\n", u, v, c);

}

void BFS(int s)//预处理出level数组

//直接BFS到每个点

{

    memset(level, -, sizeof(level));

    queue<int>q;

    level[s] = ;

    q.push(s);

    while (!q.empty())

    {

        int u = q.front();

        q.pop();

        for (int v = ; v < G[u].size(); v++)

        {

            edge& now = e[G[u][v]];

            if (now.c > now.f && level[now.v] < )

            {

                level[now.v] = level[u] + ;

                q.push(now.v);

            }

        }

    }

}

int dfs(int u, int t, int f)//DFS寻找增广路

{

    if (u == t)return f;//已经到达源点，返回流量f

    for (int &v = iter[u]; v < G[u].size(); v++)

        //这里用iter数组表示每个点目前的弧，这是为了防止在一次寻找增广路的时候，对一些边多次遍历

        //在每次找增广路的时候，数组要清空

    {

        edge &now = e[G[u][v]];

        if (now.c - now.f >  && level[u] < level[now.v])

            //now.c - now.f > 0表示这条路还未满

            //level[u] < level[now.v]表示这条路是最短路，一定到达下一层，这就是Dinic算法的思想

        {

            int d = dfs(now.v, t, min(f, now.c - now.f));

            if (d > )

            {

                now.f += d;//正向边流量加d

                e[G[u][v] ^ ].f -= d;

                //反向边减d，此处在存储边的时候两条反向边可以通过^操作直接找到

                return d;

            }

        }

    }

    return ;

}

int Maxflow(int s, int t)

{

    int flow = ;

    for (;;)

    {

        BFS(s);

        if (level[t] < )return flow;//残余网络中到达不了t，增广路不存在

        memset(iter, , sizeof(iter));//清空当前弧数组

        int f;//记录增广路的可增加的流量

        while ((f = dfs(s, t, INF)) > )

        {

            flow += f;

        }

    }

    return flow;

}

bool vis[][];

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

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

int main()

{

    int n, m;

    cin >> n >> m;

    memset(vis, , sizeof(vis));

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

    {

        int x, y;

        cin >> x >> y;

        vis[x][y] = ;

    }

    int s = , t = n * n + ;

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

    {

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

        {

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

            int ex = (i - )*n + j;

            if((i+j)&)

            {

                add(s, ex, );

                for(int k=;k<;k++)

                {

                    int tx = i + dx[k];

                    int ty = j + dy[k];

                    if (tx > n || tx< || ty>n || ty < ) continue;

                    if (vis[tx][ty]) continue;

                    //printf("i=%d j=%d tx=%d ty=%d\n", i, j, tx, ty);

                    int ed = (tx - )*n + ty;

                    add(ex, ed, inf);

                }

            }

            else add(ex, t, );

        }

    }

    int ans = Maxflow(s, t);

    //printf("%d\n", ans);

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

    return ;

}