def add(x,y):
  return x + y

def e(a):
  if a == min:
    return 10**18
  if a == max:
    return -10**18
  if a == add:
    return 0

class SegTree:
  def __init__(self, segf, init_val):
    n = len(init_val)
    self.segf = segf
    self.e = e(segf)
    self.seg_len = 1 << n.bit_length()
    self.seg = [self.e] * 2*self.seg_len
    
    for i in range(n):
      self.seg[i+ self.seg_len] = init_val[i]
    for i in range(self.seg_len)[::-1]:
      self.seg[i] = segf(self.seg[i<<1], self.seg[i<<1|1])

  def point_add(self,pos,x):
    pos += self.seg_len
    self.seg[pos] += x 
    while True: 
      pos >>= 1 
      if not pos: break 
      self.seg[pos] = self.segf(self.seg[pos<<1],  self.seg[pos<<1|1])

  def point_update(self, pos, x):
    pos += self.seg_len
    self.seg[pos] = x 
    while True: 
      pos >>= 1 
      if not pos: break 
      self.seg[pos] = self.segf(self.seg[pos<<1],  self.seg[pos<<1|1])

  def get_range(self,l,r):
    l += self.seg_len; r += self.seg_len
    res = self.e
    while l < r: 
      if l & 1: 
        res = self.segf(res, self.seg[l])
        l += 1 
      if r & 1: 
        r -= 1 
        res = self.segf(res, self.seg[r])
      l >>= 1; r >>= 1
    return res
  
  # ------ range_add & get_point -------
  def range_add(self, l,r,x):
    l += self.seg_len; r += self.seg_len
    self.seg[l] += x
    self.seg[r] += x
    while l < r: 
      if l & 1: 
        self.seg[l] = self.segf(x,self.seg[l])
        l += 1 
      if r & 1: 
        r -= 1 
        self.seg[r] = self.segf(x,self.seg[r])
      l >>= 1; r >>= 1

  def get_point(self,pos):
    pos += self.seg_len
    res = self.seg[pos]
    while True: 
      pos >>=1
      if not pos: break
      res = self.segf(res, self.seg[pos])
    return res
  
mod = 998244353
h,w,n,p = map(int,input().split())
xy = [list(map(int,input().split())) for i in range(n)]
xx = [[] for i in range(h+1)]
for x,y in xy:
  xx[x].append(y)

for i in range(1, h+1):
  xx[i].sort(key = lambda x : -x)

st = SegTree(max, [0]*(w+1))

for i in range(1, h+1):
  xxi = xx[i]
  for y in xxi:
    tmp = st.get_range(0, y+1)
    tmp += 1
    st.point_update(y, tmp)
  
cnt = st.get_range(0, w+1)

ex1 = (p-1)*pow(p, mod-2, mod)
ex2 = (p-2)*pow(p, mod-2, mod)

ans = 1 - pow(ex1, h+w-1-cnt-2, mod) * pow(ex2, cnt, mod)%mod
ans %= mod
print(ans)