#include <bits/stdc++.h>   using namespace std;   const int N = 3050;   int F[N][N];   char buf[N];   vector<int> row[N];   short S[N][N];   inline short get(int y1, int x1, int y2, int x2) {     return S[y2][x2] + S[y1][x1] - S[y2][x1] - S[y1][x2];   }   int A[N];   int n, m, k;   short to_L[N], to_R[N];   short path[N];   int pt = 0;   inline short getL(short x) {     if (x == -1) return -1;     if (to_L[x] == -1 || A[to_L[x]]) return to_L[x];     pt = 0;     path[pt++] = x;     while (true) {       x = to_L[x];       if (x == -1 || A[x] != 0)         break;       else         path[pt++] = x;     }     for (int i = 0; i < pt - 1; i++) to_L[path[i]] = x;     return x;   }   short getR(short x) {     if (x == m) return m;     if (to_R[x] == m || A[to_R[x]]) return to_R[x];     pt = 0;     path[pt++] = x;     while (true) {       x = to_R[x];       if (x == m || A[x] != 0)         break;       else         path[pt++] = x;     }     for (int i = 0; i < pt - 1; i++) to_R[path[i]] = x;     return x;   }   vector<short> visited;   short Rpos[N];   int used[N];   int curver = 0;   vector<short> interesting;   void calcLpos(short x) {     visited.clear();     short cur = 0;     while (true) {       if (x == -1) return;       if (used[x] == curver) return;       used[x] = curver;       visited.push_back(x);       cur += A[x];       if (cur >= k) {         x = getL(x);         if (x != -1 && used[x] != curver) visited.push_back(x), used[x] = curver;         return;       }       x = getL(x);     }     assert(false);   }   long long start(short r) {     for (short j = 0; j < m; j++) {       A[j] = get(r, j, n, j + 1);     }     short lst = m;     for (short j = m - 1; j >= 0; j--) {       to_R[j] = lst;       if (A[j]) lst = j;     }     lst = -1;     for (short j = 0; j < m; j++) {       to_L[j] = lst;       if (A[j]) lst = j;     }     lst = -1;     for (short j = 0; j < m; j++) {       if (A[j]) {         Rpos[j] = max(j, lst);         while (true) {           short nrpos = getR(Rpos[j]);           if (Rpos[j] == m || get(r, j, n, Rpos[j] + 1) >= k) {             break;           } else {             Rpos[j] = nrpos;           }         }         lst = Rpos[j];       }     }     int curval = 0;     for (short j = 0; j < m; j++) {       if (A[j]) {         short pj = getL(j);         short from = Rpos[j];         curval += (int)(j - pj) * (m - from);       }     }     long long ans = 0;     ans += curval;     for (int i = n - 1; i > r; i--) {       interesting.clear();       ++curver;       for (short x : row[i]) {         calcLpos(x);         interesting.insert(interesting.end(), visited.rbegin(), visited.rend());         short r = getR(x);         if (r != m && used[r] != curver) {           used[r] = curver;           interesting.push_back(r);         }       }       for (short j : interesting) {         short pj = getL(j);         short from = Rpos[j];         curval -= (int)(j - pj) * (m - from);       }       for (short x : row[i]) {         A[x]--;       }       short lst = -1;       for (short j : interesting) {         if (!A[j]) continue;         short pj = getL(j);         Rpos[j] = max(Rpos[j], lst);         while (true) {           short nrpos = getR(Rpos[j]);           if (Rpos[j] == m || get(r, j, i, Rpos[j] + 1) >= k) {             break;           } else {             Rpos[j] = nrpos;           }         }         lst = Rpos[j];         short from = Rpos[j];         curval += (int)(j - pj) * (m - from);       }       ans += curval;     }     return ans;   }   int main() {     int tmp;     scanf( %d %d %d %d  , &n, &m, &tmp, &k);     for (int i = 0; i < tmp; i++) {       int y, x;       scanf( %d %d , &y, &x);       --y, --x;       F[y][x] = 1;       row[y].push_back(x);     }     for (int i = 0; i < n; i++) {       sort(row[i].begin(), row[i].end());     }     for (int i = 0; i < n; i++) {       for (int j = 0; j < m; j++) {         S[i + 1][j + 1] = S[i + 1][j] + S[i][j + 1] - S[i][j] + F[i][j];       }     }     long long ans = 0;     long long last = start(n - 1);     ans = last;     for (int i = n - 2; i >= 0; i--) {       if (i % 10 == 0) {       }       if (row[i].empty())         ans += last;       else {         ans += (last = start(i));       }     }     printf( %lld n , ans);   }