1 #include <iostream>
 2 #include <iomanip>
 3 #include <cstdlib>
 4 #include <cstdio>
 5 #include <algorithm>
 6 #include <cstring>
 7 #include <cmath>
 8 #include <string>
 9 #define MIN(a,b) a<b?a:b
10 #define RG register
11 const int inf = 2147483641;
12 const int M = 50000;
13 const int N = 1000000;
14 
15 using namespace std;
16 
17 int gi(){
18     char ch=getchar();int x=0;
19     while(ch<‘0‘ || ch>‘9‘) ch=getchar();
20     while(ch>=‘0‘ && ch<=‘9‘) x=x*10+ch-‘0‘,ch=getchar();
21     return x;
22 }
23 
24 int f[N],cnt=1,vis[205][205],S,T,dis[N],ans,nxt[N],head[N];
25 int z[8]={-2,-2,-1,-1,1,1,2,2},y[8]={-1,1,-2,2,-2,2,-1,1};
26 
27 struct date{
28     int from,to,val;
29 }nn[N];
30 
31 void link(int l,int r,int val){
32     nn[++cnt]=(date){l,r,val},nxt[cnt]=head[l],head[l]=cnt;
33     nn[++cnt]=(date){r,l,0},nxt[cnt]=head[r],head[r]=cnt;
34     return;
35 }
36 
37 int bfs(){
38     for (RG int i=S; i<=T; ++i) dis[i]=0;
39     int l=0,r=1;
40     f[1]=0,dis[0]=1;
41     while(l<r){
42         ++l;
43         for (RG int i=head[f[l]]; i; i=nxt[i])
44             if (nn[i].val && dis[nn[i].to]==0){
45                 dis[nn[i].to]=dis[f[l]]+1;
46                 f[++r]=nn[i].to;
47             }
48         if (dis[T]) return 1;
49     }
50     return 0;
51 }
52 
53 int dinic(int xh,int sum){
54     int s=0;
55     if (xh==T) return sum;
56     for (RG int i=head[xh]; i; i=nxt[i])
57         if (nn[i].val && dis[nn[i].to]==dis[xh]+1){
58             RG int tmp=dinic(nn[i].to,MIN(sum,nn[i].val));
59             nn[i].val-=tmp,nn[i^1].val+=tmp,s+=tmp,sum-=tmp;
60             if (sum==0) break;
61         }
62     if (s==0) dis[xh]=-1;
63     return s;
64 }
65 
66 int main(){
67     freopen("x.in","r",stdin);
68     freopen("x.out","w",stdout);
69     RG int n=gi(),m=gi();T=n*n+1;
70     for (RG int i=1; i<=m; ++i){
71         RG int l=gi(),r=gi();
72         vis[l][r]=1;
73     }
74     for (RG int i=1; i<=n; ++i){
75         RG int s=(i-1)*n;
76         for (RG int j=1; j<=n; ++j)
77             for (RG int k=0; k<=7; ++k) if ((i+j)&1){
78                     RG int xi=i+z[k],yi=j+y[k],g=(xi-1)*n;
79                     if (xi<=n && xi>0 && yi>0 && yi<=n)
80                         link(s+j,g+yi,1);
81                 }
82     }
83     for (RG int i=1; i<=n; ++i){
84         RG int s=(i-1)*n;
85         for (RG int j=1; j<=n; ++j)
86             if ((i+j)&1)
87                 link(S,s+j,vis[i][j]^1);
88             else
89                 link(s+j,T,vis[i][j]^1);
90     }
91     while(bfs())
92         ans+=dinic(S,inf);
93     printf("%d",n*n-ans-m);
94     return 0;
95 }