from sys import stdin
input = stdin.readline
from bisect import bisect_left, bisect_right

MOD = 998244353

def inverse(n, d):
    return n * pow(d, -1, MOD) % MOD

H, W, N, P = map(int, input().split())
XY = sorted([list(map(int, input().split())) for _ in range(N)])

stack = []
for X, Y in XY:
    b = bisect_right(stack, Y)
    if b < len(stack):
        stack[b] = Y
    else:
        stack.append(Y)

a, b = H+W-3-len(stack), len(stack)
print((1-pow(inverse(P-1, P), a, MOD)*pow(inverse(P-2, P), b, MOD)%MOD)%MOD)