import sys
input = sys.stdin.readline
H, W, N, P = map(int, input().split())
mod = 998244353
a = [[] for _ in range(H + 1)]

for _ in range(N):
  x, y = map(int, input().split())
  a[x].append(y)

class SegTree:
  def segfunc(self, x, y):
    return max(x, y)
  def __init__(self, n, ide_ele, init_val):
    #####単位元######
    self.ide_ele = ide_ele
    #num:n以上の最小の2のべき乗
    self.num = 2 ** (n - 1).bit_length()
    self.seg = [self.ide_ele] * 2 * self.num
    #set_val
    for i in range(n):
      self.seg[i + self.num - 1] = init_val[i]    
    #built
    for i in range(self.num - 2, -1, -1) :
      self.seg[i] = self.segfunc(self.seg[2 * i + 1], self.seg[2 * i + 2]) 
  def update(self, k, x):
    k += self.num - 1
    self.seg[k] = x
    while k + 1:
      k = (k - 1) // 2
      self.seg[k] = self.segfunc(self.seg[k * 2 + 1], self.seg[k * 2 + 2]) 
  def query(self, p, q):
    if q <= p:
      return self.ide_ele
    p += self.num - 1
    q += self.num - 2
    res = self.ide_ele
    while q - p > 1:
      if p & 1 == 0:
        res = self.segfunc(res, self.seg[p])
      if q & 1 == 1:
        res = self.segfunc(res, self.seg[q])
        q -= 1
      p = p // 2
      q = (q - 1) // 2
    if p == q:
      res = self.segfunc(res, self.seg[p])
    else:
      res = self.segfunc(self.segfunc(res, self.seg[p]), self.seg[q])
    return res

seg = SegTree(W + 1, 0, [0] * (W + 1))

for x in range(H, -1, -1):
  s = []
  a[x].sort(reverse = True)
  for y in a[x]:
    q = seg.query(y, W + 1)
    seg.update(y, q + 1)

  #print(s)
q = seg.query(0, W + 1)
res = pow(P - 2, q, mod) * pow(P, (mod - 2) * q, mod)
res %= mod
res *= pow(P - 1, (H + W - 3 - q), mod) * pow(P, (mod - 2) * (H + W - 3 - q), mod)
res %= mod
res = 1 - res
res %= mod
print(res)