#include <bits/stdc++.h>   using namespace std;   template <class T>   T min(T a, T b, T c) {     return min(a, min(b, c));   }   template <class T>   T max(T a, T b, T c) {     return max(a, max(b, c));   }   int r, c, k, n, a[15][15];   int main() {     scanf( %d%d%d%d , &r, &c, &n, &k);     for (int i = (1); i <= (n); ++i) {       int x, y;       scanf( %d%d , &x, &y);       a[x][y] = 1;     }     int ans = 0;     for (int x1 = (1); x1 <= (r); ++x1) {       for (int y1 = (1); y1 <= (c); ++y1) {         for (int x2 = (x1); x2 <= (r); ++x2) {           for (int y2 = (y1); y2 <= (c); ++y2) {             int sum = 0;             for (int x = (x1); x <= (x2); ++x) {               for (int y = (y1); y <= (y2); ++y) sum += a[x][y];             }             if (sum >= k) ++ans;           }         }       }     }     cout << ans;     return 0;   }   