#include <bits/stdc++.h>   using namespace std;   int r, c, n, k, x, y;   int flag[101][101];   int main() {     cin >> r >> c >> n >> k;     for (int i = 0; i < n; i++) {       cin >> x >> y;       flag[x][y] = 1;     }     int cnt = 0;     for (int i = 1; i <= r; i++) {       for (int i1 = 1; i1 <= c; i1++) {         for (int i2 = 1; i2 <= r; i2++) {           for (int i3 = 1; i3 <= c; i3++) {             int sum = 0;             for (int i5 = i; i5 <= i2; i5++) {               for (int i6 = i1; i6 <= i3; i6++) {                 if (flag[i5][i6] == 1) sum++;               }             }             if (sum >= k) cnt++;           }         }       }     }     cout << cnt;     return 0;   }   