#include <stdio.h>
#include <stdlib.h>

int cmp (const void *a, const void *b) {
  int *a_ = (int *)a;
  int *b_ = (int *)b;
  
  if (a_[0] > b_[0]) {
    return 1;
  }
  
  if (a_[0] < b_[0]) {
    return -1;
  }
  
  if (a_[1] > b_[1]) {
    return 1;
  }
  
  if (a_[1] < b_[1]) {
    return -1;
  }
  
  return 0;
}

long long power_mod (long long a, long long b, long long mod_num) {
  long long ans = 1LL;
  
  if (b > 0LL) {
    ans = power_mod(a, b/2LL, mod_num);
    ans = (ans * ans) % mod_num;
    if (b%2LL == 1LL) {
      ans = (ans * (a % mod_num)) % mod_num;
    }
  }
  
  return ans;
}

void set_segt (int *t, int idx, int val, int size) {
  idx = idx+size-1;
  t[idx] = val;
  
  while (idx > 0) {
    idx = (idx-1)/2;
    t[idx] = t[2*idx+1];
    if (t[2*idx+2] > t[idx]) {
      t[idx] = t[2*idx+2];
    }
  }
  
  return;
}

int max_segt_rec (int *t, int a, int b, int k, int l, int r) {
  int ans = 0;
  int tmp = 0;
  
  if (r <= a || b <= l) {
    return 0;
  }
  
  if (a <= l && r <= b) {
    return t[k];
  }
  
  ans = max_segt_rec(t, a, b, 2*k+1, l, (l+r)/2);
  tmp = max_segt_rec(t, a, b, 2*k+2, (l+r)/2, r);
  
  if (tmp > ans) {
    ans = tmp;
  }
  
  return ans;
}

int max_segt (int *t, int a, int b, int size) {
  return max_segt_rec(t, a, b, 0, 0, size);
}

int main () {
  int h = 0;
  int w = 0;
  int n = 0;
  long long p = 0LL;
  int xy[200000][2] = {};
    
  int res = 0;
  
  long long ans = 0LL;
  long long mod_num = 998244353LL;
  
  int max = 0;
  
  int t[600000] = {};
  int size = 1;
  
  res = scanf("%d", &h);
  res = scanf("%d", &w);
  res = scanf("%d", &n);
  res = scanf("%lld", &p);
  for (int i = 0; i < n; i++) {
    res = scanf("%d", xy[i]);
    res = scanf("%d", xy[i]+1);
  }
  
  qsort(xy, n, sizeof(int)*2, cmp);
  
  while (size <= w) {
    size <<= 1;
  }
  
  for (int i = 0; i < n; i++) {
    int tmp = max_segt(t, 0, xy[i][1]+1, size);
    set_segt(t, xy[i][1], tmp+1, size);
  }
  
  max = max_segt(t, 0, w+1, size);
  
  ans = power_mod(p-2LL, (long long)max, mod_num);
  ans *= power_mod(p-1LL, (long long)(h+w-3-max), mod_num);
  ans %= mod_num;
  ans *= power_mod(p, ((long long)(h+w-3))*(mod_num-2LL), mod_num);
  ans %= mod_num;
  
  ans = 1LL+mod_num-ans;
  ans %= mod_num;
  
  printf("%lld\n", ans);
  return 0;
}