H,W,N,P = map(int,input().split())
dat = [[0] * W for _ in range(H)]
for _ in range(N):
    x,y = map(int,input().split())
    dat[x-1][y-1] = 1
dp = [[-1] * W for _ in range(H)]
dp[0][0] = 0
#memo = [[0] * W for _ in range(H)]
from collections import deque
stack = deque([(0,0)])
while stack:
    x,y = stack.popleft()
    for i,j in [(1,0),(0,1)]:
        if x + i < H and y + j < W:
            if dp[x + i][y + j] == -1:
                stack.append((x + i,y + j))
            t = dp[x][y] + dat[x + i][y + j]
            if t > dp[x + i][y + j]:
                dp[x + i][y + j] = t
u = dp[-1][-1]
mod = 998244353
v = H + W - 3 - u
r = pow(P,mod-2,mod)
tmp = pow((1-r)%mod,v,mod)*pow((1-r * 2)%mod,u,mod)
ans = (1-tmp)%mod
print(ans)