#include <bits/stdc++.h>   using namespace std;   template <typename T1, typename T2>   void chkmin(T1 &x, T2 y) {     if (x > y) x = y;   }   template <typename T1, typename T2>   void chkmax(T1 &x, T2 y) {     if (x < y) x = y;   }   namespace fastio {   char rbuf[1 << 23], *p1 = rbuf, *p2 = rbuf, wbuf[1 << 23], *p3 = wbuf;   inline char getc() {     return p1 == p2 &&                    (p2 = (p1 = rbuf) + fread(rbuf, 1, 1 << 23, stdin), p1 == p2)                ? -1                : *p1++;   }   inline void putc(char x) { (*p3++ = x); }   template <typename T>   void read(T &x) {     x = 0;     char c = getchar();     T neg = 0;     while (!isdigit(c)) neg |= !(c ^  - ), c = getchar();     while (isdigit(c)) x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();     if (neg) x = (~x) + 1;   }   template <typename T>   void recursive_print(T x) {     if (!x) return;     recursive_print(x / 10);     putc(x % 10 ^ 48);   }   template <typename T>   void print(T x) {     if (!x) putc( 0 );     if (x < 0) putc( - ), x = ~x + 1;     recursive_print(x);   }   void print_final() { fwrite(wbuf, 1, p3 - wbuf, stdout); }   }  // namespace fastio   const int MAXN = 3e3;   int R, C, n, k, x[MAXN + 5], y[MAXN + 5];   vector<int> vr[MAXN + 5], vc[MAXN + 5];   int l[MAXN + 5], r[MAXN + 5];   long long ans = 0;   int main() {     scanf( %d%d%d%d , &R, &C, &n, &k);     for (int i = 1; i <= n; i++) {       scanf( %d%d , &x[i], &y[i]);       vr[x[i]].push_back(i);       vc[y[i]].push_back(i);     }     for (int i = 1; i <= MAXN; i++)       sort(vr[i].begin(), vr[i].end(),            [](int lhs, int rhs) { return y[lhs] > y[rhs]; });     for (int i = 1; i <= MAXN; i++)       sort(vc[i].begin(), vc[i].end(),            [](int lhs, int rhs) { return x[lhs] < x[rhs]; });     for (int i = 1; i <= R; i++) {       memset(l, 0, sizeof(l));       memset(r, 0, sizeof(r));       int pre = 0;       for (int j = 1; j <= C; j++)         for (int t = 0; t < vc[j].size(); t++)           if (x[vc[j][t]] >= i) {             int id = vc[j][t];             l[id] = pre;             if (pre) r[pre] = id;             pre = id;           }       long long ret = 0;       for (int j = 1; j <= C; j++)         for (int t = 0; t < vc[j].size(); t++)           if (x[vc[j][t]] >= i) {             int id = vc[j][t], cur = id;             for (int stp = 1; stp < k; stp++) cur = r[cur];             if (cur) ret += 1ll * (C - y[cur] + 1) * (y[id] - y[l[id]]);           }       ans += ret;       for (int j = R; j >= i; j--) {         for (int t = 0; t < vr[j].size(); t++) {           int id = vr[j][t];           if (!r[id]) {             int cur = id;             for (int stp = 1; stp < k; stp++) cur = l[cur];             if (cur) ret -= 1ll * (y[cur] - y[l[cur]]) * (C - y[id] + 1);             if (r[id]) l[r[id]] = l[id];             if (l[id]) r[l[id]] = r[id];             continue;           }           int cr = r[id], cl = r[id], stp = 0;           while (stp < k - 1) {             if (!r[cr]) break;             cr = r[cr];             ++stp;           }           for (int o = 1; o <= k - 1 - stp; o++) cl = l[cl];           if (cl) ret -= 1ll * (C - y[cr] + 1) * (y[cl] - y[l[cl]]);           for (int o = 1; o <= stp + 1; o++) {             cr = l[cr];             cl = l[cl];             if (cl) ret -= 1ll * (C - y[cr] + 1) * (y[cl] - y[l[cl]]);           }           if (r[id]) l[r[id]] = l[id];           if (l[id]) r[l[id]] = r[id];           if (!r[id]) continue;           cr = r[id], cl = r[id], stp = 0;           while (stp < k - 1) {             if (!r[cr]) break;             cr = r[cr];             ++stp;           }           for (int o = 1; o <= k - 1 - stp; o++) cl = l[cl];           if (cl) ret += 1ll * (C - y[cr] + 1) * (y[cl] - y[l[cl]]);           for (int o = 1; o <= stp; o++) {             cr = l[cr];             cl = l[cl];             if (cl) ret += 1ll * (C - y[cr] + 1) * (y[cl] - y[l[cl]]);           }         }         ans += ret;       }     }     printf( %lld n , ans);     return 0;   }