from collections import defaultdict

class Segtree():
    def __init__(self):
        self.tree = [-1 * 10 ** 9 for _ in range(1 << 19)]

    def set(self, n, k):
        n += (1 << 18)
        ret = -1 * (10 ** 9)
        
        now = n
        self.tree[now] = k
        while now > 1:
            now = now // 2
            self.tree[now] = max(self.tree[now * 2], self.tree[now * 2 + 1])

    def out(self, x):
        print(self.tree[(1 << 18) : (1 << 18) + x])        
    
    def get(self, n):
        return self.tree[n + (1 << 18)]
    
    def prod(self, l, r):
        l += (1 << 18)
        r += (1 << 18)
        if l >= r:
            return -1 * (10 ** 9)
        
        left_ret = -1 * (10 ** 9)
        right_ret = -1 * (10 ** 9)
        while l < r:
            if l % 2 == 1:
                left_ret = max(left_ret, self.tree[l])
                l += 1
            
            if r % 2 == 1:
                r -= 1
                right_ret = max(right_ret, self.tree[r])
            
            l = l // 2
            r = r // 2
        
        return max(left_ret, right_ret)

H, W, N, P = map(int, input().split())
sy = set()
sy.add(1)
plst = []
for i in range(N):
    x, y = map(int, input().split())
    sy.add(y)
    plst.append([x, y])

plst.sort()
#print(plst)

ly = list(sy)
ly.sort()

#print(ly)

d = defaultdict(int)
for i in range(len(ly)):
    d[ly[i]] = i

seg = Segtree()

seg.set(d[1], 0)

for i in range(N):
    vy = d[plst[i][1]]
    val = seg.get(vy)
    prd = seg.prod(0, vy + 1)
    seg.set(vy, max(prd, val) + 1)

max_omen = seg.prod(0, (1 << 18))

mod = 998244353

def inv(p):
    return pow(p, mod - 2, mod)

ans = 1

ans = (ans * pow(P - 1, H + W - 3 - max_omen, mod)) % mod
ans = (ans * pow(P - 2, max_omen, mod)) % mod

ans = (pow(P, H + W - 3, mod) - ans + mod) % mod

ans = (ans * inv(pow(P, H + W - 3, mod))) % mod
print(ans)