#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<numeric>
#include<functional>
#include<complex>

using namespace std;
#define BET(a,b,c) ((a)<=(b)&&(b)<(c))
#define FOR(i,n) for(int i=0,i##_end=(int(n));i<i##_end;i++)
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(),(x).end()
#define MP make_pair
#define FOR_EACH(it,v) for(__typeof(v.begin()) it=v.begin(),it_end=v.end() ; it != it_end ; it++)
typedef vector<int> VI;
typedef vector<VI> VVI;

int main()
{
    int W,H,N;
    cin>>W>>H>>N;
    VI S(N),K(N);
    FOR(i,N){
        cin>>S[i]>>K[i];
    }
    sort(ALL(S)); S.erase(unique(S.begin(),S.end()),S.end());
    sort(ALL(K)); K.erase(unique(K.begin(),K.end()),K.end());
    long long ans = 1LL * W * H - (1LL * (W - SZ(S)) * (H - SZ(K))) - N ;
    cout<<ans<<endl;
    return 0;
}