#include<bits/stdc++.h>
#define INF LLONG_MAX/2
#define N 40050
using namespace std;struct ss
{int v,next;long long flow;
};
int head[N],now_edge=0,S,T;
ss edg[N*32];void init()
{now_edge=0;memset(head,-1,sizeof(head));
}void addedge(int u,int v,long long flow)
{edg[now_edge]=(ss){v,head[u],flow};head[u]=now_edge++;edg[now_edge]=(ss){u,head[v],0};head[v]=now_edge++;
}int dis[N];int bfs()
{memset(dis,0,sizeof(dis));queue<int>q;q.push(S);dis[S]=1;while(!q.empty()){int now=q.front();q.pop();for(int i=head[now];i!=-1;i=edg[i].next){ss &e=edg[i];if(e.flow>0&&dis[e.v]==0){dis[e.v]=dis[now]+1;q.push(e.v);}}}if(dis[T]==0)return 0;return 1;
}int current[N];
long long dfs(int x,long long maxflow)
{if(x==T)return maxflow;for(int i=current[x];i!=-1;i=edg[i].next){current[x]=i;ss &e=edg[i];if(e.flow>0&&dis[e.v]==dis[x]+1){long long flow=dfs(e.v,min(maxflow,e.flow));if(flow!=0){e.flow-=flow;edg[i^1].flow+=flow;return flow;}}}return 0;
}long long dinic()
{long long ans=0,flow;while(bfs()){for(int i=0;i<N;i++)current[i]=head[i];while(flow=dfs(S,INF))ans+=flow;}return ans;
}int color[205][205]={0};
int num[205][205];
int Map[205][205]={0};
int n;int check(int x,int y)
{if(x<=0||x>n||y<=0||y>n||Map[x][y])return 0;return 1;
}int fx[10]={-2,-2,-1,1,2,2,1,-1};
int fy[10]={-1,1,2,2,1,-1,-2,-2};int main()
{init();int m,cnt=1;scanf("%d %d",&n,&m);for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)num[i][j]=cnt++;S=cnt;T=S+1;for(int i=1;i<=n;i++)for(int j=(i%2==0 ? 2 : 1);j<=n;j+=2)color[i][j]=1;/*    for(int i=1;i<=n;i++){for(int j=1;j<=n;j++)printf("%d",color[i][j]);printf("\n");}*/for(int i=1;i<=m;i++){int x,y;scanf("%d %d",&x,&y);Map[x][y]=1;}for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)if(!Map[i][j]&&color[i][j]){for(int k=0;k<8;k++)if(check(i+fx[k],j+fy[k])){addedge(num[i][j],num[i+fx[k]][j+fy[k]],INF);}}for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)if(!Map[i][j]){if(color[i][j])addedge(S,num[i][j],1);elseaddedge(num[i][j],T,1);}printf("%lld\n",(long long)n*n-dinic()-m);return 0;}