#include <bits/stdc++.h>
#define LL long long
using namespace std;
const int MAXN=40005,MAXM=400005;
const LL INF=1e17,MXD=1e7;
int N,M,S,T,K,et=1;
const int dx[8]={1,1,-1,-1,3,3,-3,-3};
const int dy[8]={3,-3,3,-1,1,-1,1,-1};
struct Edge
{
	int to,nxt;
	LL fl;
}e[MAXM<<1];
int hd[MAXN],dep[MAXN],cur[MAXN];
void Add(int u,int v,LL fl)
{
	e[++et]={v,hd[u],fl};
//	printf("!%d %d %d %lld\n",u,v,hd[u],fl);
	hd[u]=et;
	e[++et]={u,hd[v],0};
	hd[v]=et;
	return;
}
bool bfs()
{
	for(int i=1;i<=N*M+2;i++) dep[i]=MXD;
	dep[S]=0;
	queue<int>q;
	q.push(S);
	while(q.size())
	{
		int u=q.front();
//		printf("BFS%d\n",u);
		if(u==T) return 1;
		q.pop();
		for(int i=hd[u];i;i=e[i].nxt)
		{
			int v=e[i].to;
			LL fl=e[i].fl;
		//	printf("BFS%d %d %lld %d\n",u,v,fl,dep[v]);
			if(fl>0&&dep[v]==MXD)
			{
				dep[v]=dep[u]+1;
			//	puts("OOO");
				q.push(v);
			}
		}
	}
	return 0;
}
LL dfs(int u,LL flow)
{
//	printf("DFS%d %lld\n",u,flow);
	if(u==T||flow==0) return flow;
	LL res=0;
	for(int i=cur[u];i;i=e[i].nxt)
	{
		cur[u]=i;
		int v=e[i].to;
		LL fl=e[i].fl;
		if(fl<=0||dep[v]!=dep[u]+1) continue;
		LL k=dfs(v,min(flow,fl));
		e[i].fl-=k;
		e[i^1].fl+=k;
		res+=k;
		flow-=k;
	}
	return res;
}
LL Dinic()
{
	LL res=0;
	while(bfs())
	{
		for(int i=1;i<=N*M+2;i++) cur[i]=hd[i];
		res+=dfs(S,INF);
	}
	return res;
}
int Trans(int x,int y)
{
	return (x-1)*M+y;
}
bool b[MAXN];
int main()
{
	scanf("%d %d %d",&N,&M,&K);
	for(int i=1;i<=K;i++)
	{
		int x,y;
		scanf("%d %d",&x,&y);
		b[Trans(x,y)]=1;
	}
	K=0;
	for(int i=1;i<=N;i++)
	{
		for(int j=1;j<=M;j++)
		{
			if(i%2) Add(N*M+1,Trans(i,j),1);
			else Add(Trans(i,j),N*M+2,1);
			if(b[Trans(i,j)]) K++;
		}
	}
	for(int i=1;i<=N;i++)
	{
		if(i%2==0) continue;
		for(int j=1;j<=M;j++)
		{
			for(int k=0;k<8;k++)
			{
				int x=i+dx[k],y=j+dy[k];
				if(x<1||x>N||y<1||y>M) continue;
				if(b[Trans(i,j)]||b[Trans(x,y)]) continue;
				Add(Trans(i,j),Trans(x,y),1);
			}
		}
	}
	S=N*M+1,T=N*M+2;
	printf("%lld\n",N*M-K-Dinic());
	return 0;
}

是建模的问题吗