#include <bits/stdc++.h>
using namespace std;
int n,m,k,s;
int x,y,cnt;
int L[500005],R[500005],U[500005],D[500005];//L/R\U|D-
int main(){
    cin >> n >> m >> k;
    s=n+m;
    for(int i = 1;i <= k;i++){
        cin >> x >> y;
        L[s+(x+y)]=1;
        R[s+(x-y)]=1;
        U[x]=1;
        D[y]=1;
    }
    for(int i = 1;i <= n;i++){
        for(int j = 1;j <= m;j++){
            if(L[s+i+j]||R[s+i-j]||U[i]||D[j])continue;
            cnt++;
        }
    }
    cout  << cnt << endl;
    return 0;
}