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#include <queue>
#include <iostream>
#include <vector>
#include <cstring>
#include <iostream>
#include <set>
#include <cstring>
#include <stack>
#include <algorithm>
//#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 3e5 + 10;
const ll INF = 3e16 + 10;

struct node {
    int y, x1, x2;
    bool up;
    node () {}
    node(int _y, int _x1, int _x2, bool _up) {
        y = _y;
        x1 = _x1;
        x2 = _x2;
        up = _up;
    }
    bool operator < (const node &tmp) const {
        return y < tmp.y;
    }
};
int main() {
    ios_base::sync_with_stdio(false);
    int L, W;
    cin >> L >> W;
    int months;
    cin >> months;
    int n;
    cin >> n;
    vector<pair<int, int>> buildings(n);
    vector<node> v;
    for(int i = 0; i < n; i++) {
        cin >> buildings[i].first >> buildings[i].second;
        
        v.push_back(node(max(1, buildings[i].second - months), max(1, buildings[i].first - months), min(L, buildings[i].first + months), true));
        v.push_back(node(min(W, buildings[i].second + months), max(1, buildings[i].first - months), min(L, buildings[i].first + months), false));
    }
    sort(v.begin(), v.end());
    stack<int> st;
    ll result = 0;
    for(int x = 1; x <= L; x++) {
        int st_max = 0;

for(int i = 0; i < (int) v.size(); i++) {
            if(v[i].x1 <=  x and x <= v[i].x2) {
                if(v[i].up) {
                    st.push(v[i].y);
                }
                else {
                    if(st.size() == 1) {
                        result += v[i].y - max(st.top(), st_max) + 1;
                        st_max = v[i].y + 1;
                    }
                    st.pop();
                }
            }
        }
        
    }
    cout << result << endl;
    return 0;
}