## https://yukicoder.me/problems/no/2435

MOD = 998244353


class SegmentTree:
    """
    非再帰版セグメント木。
    更新は「加法」、取得は「最大値」のもの限定。
    """

    def __init__(self, init_array):
        n = 1
        while n < len(init_array):
            n *= 2
        
        self.size = n
        self.array = [0] * (2 * self.size)
        for i, a in enumerate(init_array):
            self.array[self.size + i] = a
        
        end_index = self.size
        start_index = end_index // 2
        while start_index >= 1:
            for i in range(start_index, end_index):
                self.array[i] = max(self.array[2 * i], self.array[2 * i + 1])
            end_index = start_index
            start_index = end_index // 2

    def set(self, x, a):
        index = self.size + x
        self.array[index] = a
        while index > 1:
            index //= 2
            self.array[index] = max(self.array[2 * index], self.array[2 * index + 1])

    def get_max(self, l, r):
        L = self.size + l; R = self.size + r

        # 2. 区間[l, r)の最大値を求める
        s = 0
        while L < R:
            if R & 1:
                R -= 1
                s = max(s, self.array[R])
            if L & 1:
                s = max(s, self.array[L])
                L += 1
            L >>= 1; R >>= 1
        return s


def main():
    H, W, N, P = map(int, input().split())
    xy = []
    for _ in range(N):
        x, y = map(int, input().split())
        xy.append((x - 1, y - 1))

    h_array = [[] for _ in range(H)]
    for x, y in xy:
        h_array[x].append(y)
    
    for h in range(H):
        h_array[h].sort()

    seg_tree = SegmentTree([0] * W)
    for h in  range(H):
        for w in h_array[h]:
            x = seg_tree.get_max(0, w + 1)
            y = x + 1
            seg_tree.set(w, y)
    
    x = seg_tree.get_max(0, W)

    inv_p = pow(P, MOD - 2, MOD)
    inv_px = pow(inv_p, H + W - 3, MOD)

    p1 = pow(P - 1, H + W - 3 - x, MOD)
    p2 = pow(P - 2, x, MOD)
    answer = (p1 * p2) % MOD
    answer *= inv_px
    answer %= MOD

    answer = 1 - answer
    answer %= MOD

    print(answer)





        
        



if __name__ == '__main__':
    main()