class BIT:
    def __init__(self, n):
        self.n = n; self.k = [0]*(n+1)
    def u(self, i, x):
        while i <= self.n: self.k[i] = max(self.k[i], x); i += i&-i
    def m(self, i):
        t = 0
        while i > 0: t = max(t, self.k[i]); i -= i&-i
        return t
h,w,n,p = map(int,input().split())
xy = [tuple(map(int,input().split())) for _ in range(n)]
m = 998244353; bit = BIT(w+1)
for x,y in sorted(xy): bit.u(y,bit.m(y)+1)
c = bit.m(w)
print((1-pow(p-1,h+w-3-c,m)*pow(p-2,c,m)*pow(pow(p,h+w-3,m),m-2,m))%m)