from bisect import bisect_right

MOD = 998244353

h, w, n, P = map(int, input().split())
xy = [list(map(int, input().split())) for _ in range(n)]
xy.sort(key=lambda x:(x[0] << 30) + x[1])

lst = []
for _, y in xy:
    p = bisect_right(lst, y)
    if len(lst) == p:
        lst.append(y)
    else:
        lst[p] = y

inv = pow(P, MOD - 2, MOD)
x = len(lst)
y = h + w - 3 - x
ans = 1 - pow(1 - inv, y, MOD) * pow(1 - 2 * inv, x, MOD)
print(ans % MOD)