#include <iostream>

#include <vector>

#include <cstdio>

#include <cstring>

#include <algorithm>

#include <complex>

#include <cmath>

#include <map>

#include <set>

#include <string>

#include <queue>

#include <stack>

#include <bitset>

using namespace std;

#define pb(x) push_back(x)

#define ll long long

#define mk(x, y) make_pair(x, y)

#define lson l, m, rt<<1

#define mem(a) memset(a, 0, sizeof(a))

#define rson m+1, r, rt<<1|1

#define mem1(a) memset(a, -1, sizeof(a))

#define mem2(a) memset(a, 0x3f, sizeof(a))

#define rep(i, n, a) for(int i = a; i<n; i++)

#define fi first

#define se second

typedef complex <double> cmx;

typedef pair<int, int> pll;

const double PI = acos(-1.0);

const double eps = 1e-;

const int mod = 1e9+;

const int inf = ;

const int dir[][] = { {-, }, {-, -}, {, }, {, -}, {, -}, {, }, {-, -}, {-, } };

const int maxn = 2e5;

int n, a[][];

int q[maxn*], head[], dis[], s, t, num, m;

struct node

{

    int to, nextt, c;

    node(){}

    node(int to, int nextt, int c):to(to), nextt(nextt), c(c){}

}e[maxn*];

void init() {

    num = ;

    mem1(head);

}

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

    e[num] = node(v, head[u], c); head[u] = num++;

    e[num] = node(u, head[v], ); head[v] = num++;

}

int bfs() {

    mem(dis);

    dis[s] = ;

    int st = , ed = ;

    q[ed++] = s;

    while(st<ed) {

        int u = q[st++];

        for(int i = head[u]; ~i; i = e[i].nextt) {

            int v = e[i].to;

            if(!dis[v]&&e[i].c) {

                dis[v] = dis[u]+;

                if(v == t)

                    return ;

                q[ed++] = v;

            }

        }

    }

    return ;

}

int dfs(int u, int limit) {

    if(u == t) {

        return limit;

    }

    int cost = ;

    for(int i = head[u]; ~i; i = e[i].nextt) {

        int v = e[i].to;

        if(e[i].c&&dis[v] == dis[u]+) {

            int tmp = dfs(v, min(limit-cost, e[i].c));

            if(tmp>) {

                e[i].c -= tmp;

                e[i^].c += tmp;

                cost += tmp;

                if(cost == limit)

                    break;

            } else {

                dis[v] = -;

            }

        }

    }

    return cost;

}

int dinic() {

    int ans = ;

    while(bfs()) {

        ans += dfs(s, inf);

    }

    return ans;

}

int check(int x, int y)

{

    if(x >=  && y >=  && x < n && y < n && !a[x][y])

        return ;

    return ;

}

void solve()

{

    init();

    s = n*n, t = s+;

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

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

            if(a[i][j])

                continue;

            if((i+j)%) {

                add(s, i*n+j, );

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

                    int x = i+dir[k][];

                    int y = j+dir[k][];

                    if(check(x, y)) {

                        add(i*n+j, x*n+y, );

                    }

                }

            } else {

                add(i*n+j, t, );

            }

        }

    }

    int ans = n*n-dinic()-m;

    cout<<ans<<endl;

}

int main()

{

    int x, y;

    while(~scanf("%d%d", &n, &m)) {

        mem(a);

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

            scanf("%d%d", &x, &y);

            x--;

            y--;

            a[x][y] = ;

        }

        solve();

    }

    return ;

}