#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 110;
typedef pair<int, int> PII;
#define x first
#define y second
PII match[N][N];
bool g[N][N],st[N][N];
int n,m,k;
int dx[8] = {-2, -1, 1, 2, 2, 1, -1, -2};
int dy[8] = {1, 2, 2, 1, -1, -2, -2, -1};

bool find(int x,int y)
{
    for(int i = 0;i<8;i++)
    {
        int a = x + dx[i],b = y + dy[i];
        if(a<1||a>n||b<1||b>m)continue;
        if(st[a][b] || g[a][b])continue;
        st[a][b] = true;
        auto t = match[a][b];
        if(t.x == 0 || find(t.x,t.y))
        {
            match[a][b] = {x,y};
            return true;
        }
    }
    return false;
}
int main()
{
    cin>>n>>m>>k;
    //K不能变
    // while(k--)
    // {
    //     int a,b;
    //     cin>>a>>b;
    //     g[a][b] = true;
    // }

    for (int i = 0; i < k; i ++ )
    {
        int x, y;
        cin >> x >> y;
        g[x][y] = true;
    }

    int res = 0;
    for(int i = 1;i<=n;i++)
    {
        for(int j = 1;j<=m;j++)
        {
            if (g[i][j] || (i + j) % 2) continue;
            memset(st, 0, sizeof st);
            if(find(i,j))res++;
        }
    }
    cout << n * m - k - res << endl;
    return 0;
}