#include <bits/stdc++.h>
using namespace std;
using ll=long long;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)

int main() {
    ll H,W,N;
    cin>>H>>W>>N;
    vector p(H,vector<bool>(W));
    rep(i,0,N){
        int a,b;cin>>a>>b;
        a--,b--;
        p[a][b]=1;
    }
    ll ans=0;
    vector<ll> q(W+2);
    rep(i,0,H){
        rep(j,0,W){
            q[j+1]++;
            if(p[i][j]) q[j+1]=0;
        }
        stack<int> st;
        st.push(0);
        rep(j,1,W+2){
            while((int)st.size()!=1){
                int a=st.top();
                if(q[a]<q[j]){
                    break;
                }
                st.pop();
                ll wid=j-st.top()-1;
                ll hig=q[a]-max(q[st.top()],q[j]);
                ans+=hig*(wid*(wid+1))/2;
            }
            st.push(j);
        }
    }
    cout<<ans<<"\n";
}