#include <bits/stdc++.h>
using namespace std;
const int N = 3005;
const int K = 12;
int n, m, k, bl[N][K], br[N][K], cl[K], cr[K], tl[K], tr[K];
long long ans;
char a[2][N][N];
int s[2][N][N];
inline void work(int u, int d, int l, int r, int id) {
  if (s[id][d][r] - s[id][u - 1][r] - s[id][d][l - 1] + s[id][u - 1][l - 1] ==
      0) {
    ans += (d - u + 2) * (d - u + 1) * 1ll * (r - l + 2) * (r - l + 1) / 4;
    return;
  }
  if (d - u > r - l) {
    swap(u, l);
    swap(d, r);
    id ^= 1;
  }
  int m(l + r >> 1);
  for (int i = (u); i <= (d); ++i) {
    int t(0);
    bl[i][0] = m;
    char* T = a[id][i];
    for (int j = (m); j >= (l); --j) {
      if (T[j]) bl[i][++t] = j;
      if (t == k + 1) break;
    }
    while (t < k + 1) bl[i][++t] = l - 1;
    t = 0;
    br[i][0] = m;
    for (int j = (m + 1); j <= (r); ++j) {
      if (T[j]) br[i][++t] = j;
      if (t == k + 1) break;
    }
    while (t < k + 1) br[i][++t] = r + 1;
  }
  for (int i = (u); i <= (d); ++i) {
    cl[0] = cr[0] = m;
    for (int t = 1; t <= (k + 1); ++t) cl[t] = l - 1, cr[t] = r + 1;
    for (int j = (i); j <= (d); ++j) {
      for (int t = (0); t <= (k + 1); ++t) tl[t] = cl[t], tr[t] = cr[t];
      int p(1), q(1);
      for (int t = 1; t <= (k + 1); ++t)
        if (tl[p] > bl[j][q])
          cl[t] = tl[p++];
        else
          cl[t] = bl[j][q++];
      p = 1, q = 1;
      for (int t = 1; t <= (k + 1); ++t)
        if (tr[p] < br[j][q])
          cr[t] = tr[p++];
        else
          cr[t] = br[j][q++];
      for (int t = (0); t <= (k); ++t)
        ans += (cl[t] - cl[t + 1]) * (cr[k - t + 1] - cr[0]);
    }
  }
  if (l < m) work(u, d, l, m - 1, id);
  if (m < r) work(u, d, m + 1, r, id);
}
int main() {
  int u;
  scanf("%d%d%d%d", &n, &m, &u, &k);
  for (int i = 0; i < u; ++i) {
    int x, y;
    scanf("%d%d", &x, &y);
    a[0][x][y] = 1;
    a[1][y][x] = 1;
  }
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      a[1][j][i] = a[0][i][j];
    }
  }
  for (int t = 0; t < 2; ++t) {
    for (int i = 1; i < N; ++i) {
      for (int j = 1; j < N; ++j) {
        s[t][i][j] =
            a[t][i][j] + s[t][i - 1][j] + s[t][i][j - 1] - s[t][i - 1][j - 1];
      }
    }
  }
  --k;
  work(1, n, 1, m, 0);
  long long ans2 = ans;
  cout << 1ll * (n + 1) * n / 2 * (m + 1) * m / 2 - ans2 << "\n";
  return 0;
}
