#include <bits/stdc++.h>   using namespace std;   const int INF = 1000 * 1000 * 1000;   const long long INF64 = 1LL * INF * INF;   const long long mod = INF + 7;   int m[10][10];   bool check(int k, int x, int y, int w, int h) {     int ans = 0;     for (int i = x; i <= h; ++i) {       for (int j = y; j <= w; ++j) {         ans += m[i][j];       }     }     return ans >= k;   }   void solve() {     int r, c, n, k;     cin >> r >> c >> n >> k;     for (int i = 0; i < n; ++i) {       int x, y;       cin >> x >> y;       x--;       y--;       m[x][y] = 1;     }     int ans = 0;     for (int i = 0; i < r; ++i) {       for (int j = 0; j < c; ++j) {         for (int w = j; w < c; ++w) {           for (int h = i; h < r; ++h) {             ans += check(k, i, j, w, h);           }         }       }     }     cout << ans << endl;   }   int main() {     ios_base::sync_with_stdio(false);     solve();     return 0;   }   