#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cassert>
#include<cmath>
#include<ctime>
#include<iomanip>
#include<numeric>
#include<stack>
#include<queue>
#include<map>
#include<unordered_map>
#include<set>
#include<unordered_set>
#include<bitset>
#include<random>
#include<functional>
#include<utility>
using namespace std;
template<class T,T (*op)(T,T),T (*e)()> struct segtree
{
	private:
	int size,N;
	vector<T> node;

	public:
	segtree(int N = 0) : segtree(vector<T>(N,e())) {}
	segtree(const vector<T> &V)
	{
		N = (int)V.size();
		size = 1;
		while(size < N) size <<= 1;
		node.resize(2*size);
		for(int i = 0;i < N;i++) node[i+size] = V[i];
		for(int i = size-1;i >= 1;i--) node[i] = op(node[i*2],node[i*2+1]);
	}
	void replace(int pos,T x) {func_update(pos,x,[](T u,T v){return u = v;});}
	void add(int pos,T x) {func_update(pos,x,[](T u,T v){return u + v;});}
	void func_update(int pos,T x) {func_update(pos,x,op);}
	void func_update(int pos,T x,T (*func)(T,T))
	{
		assert(0 <= pos && pos < N);
		pos += size;
		node[pos] = func(node[pos],x);
		pos >>= 1;
		while(pos)
		{
			node[pos] = op(node[pos*2],node[pos*2+1]);
			pos >>= 1;
		}
	}
	T operator[](int pos)
	{
		assert(0 <= pos && pos < N);
		return node[pos+size];
	}
	T prod(int l,int r)
	{
		assert(0 <= l && l <= r && r <= N);
		T L = e(),R = e();
		l += size,r += size;
		while(l < r)
		{
			if(l & 1) L = op(L,node[l++]);
			if(r & 1) R = op(node[--r],R);
			l >>= 1,r >>= 1;
		}
		return op(L,R);
	}
	T prod() {return node[1];}
};
int op(int a,int b) {return max(a,b);}
int e() {return 0;}
template<int m> struct modint
{
	private:
	unsigned int value;
	static constexpr int mod() {return m;}

	public:
	constexpr modint(const long long x = 0) noexcept
	{
		long long y = x;
		if(y < 0 || y >= mod())
		{
			y %= mod();
			if(y < 0) y += mod();
		}
		value = (unsigned int)y;
	}
	constexpr unsigned int val() noexcept {return value;}
	constexpr modint &operator+=(const modint &other) noexcept
	{
		value += other.value;
		if(value >= mod()) value -= mod();
		return *this;
	}
	constexpr modint &operator-=(const modint &other) noexcept
	{
		unsigned int x = value;
		if(x < other.value) x += mod();
		x -= other.value;
		value = x;
		return *this;
	}
	constexpr modint &operator*=(const modint &other) noexcept
	{
		unsigned long long x = value;
		x *= other.value;
		value = (unsigned int) (x % mod());
		return *this;
	}
	constexpr modint &operator/=(const modint &other) noexcept
	{
		return *this *= other.inverse();
	}
	constexpr modint inverse() const noexcept
	{
		assert(value);
		long long a = value,b = mod(),x = 1,y = 0;
		while(b)
		{
			long long q = a/b;
			a -= q*b; swap(a,b);
			x -= q*y; swap(x,y);
		}
		return modint(x);
	}
	constexpr modint power(long long N) const noexcept
	{
		assert(N >= 0);
		modint p = *this,ret = 1;
		while(N)
		{
			if(N & 1) ret *= p;
			p *= p;
			N >>= 1;
		}
		return ret;
	}
	constexpr modint operator+() {return *this;}
	constexpr modint operator-() {return modint() - *this;}
	constexpr modint &operator++(int) noexcept {return *this += 1;}
	constexpr modint &operator--(int) noexcept {return *this -= 1;}
	friend modint operator+(const modint& lhs, const modint& rhs) {return modint(lhs) += rhs;}
	friend modint operator-(const modint& lhs, const modint& rhs) {return modint(lhs) -= rhs;}
	friend modint operator*(const modint& lhs, const modint& rhs) {return modint(lhs) *= rhs;}
	friend modint operator/(const modint& lhs, const modint& rhs) {return modint(lhs) /= rhs;}
	friend ostream &operator<<(ostream &os,const modint &x) {return os << x.value;}
};
using mint = modint<998244353>;
/* using mint = modint<1000000007>; */


int H,W,N,P;
vector<int> G[2 << 17];
void solve()
{
	cin >> H >> W >> N >> P;
	for(int i = 0;i < N;i++)
	{
		int u,v;
		cin >> u >> v;
		u--; v--;
		G[u].push_back(v);
	}
	segtree<int,op,e> seg(W);
	for(int i = 0;i < H;i++)
	{
		vector<int> cur(G[i].size());
		for(int j = 0;j < (int)G[i].size();j++) cur[j] = seg.prod(0,G[i][j]+1);
		for(int j = 0;j < (int)G[i].size();j++) seg.replace(G[i][j],cur[j]+1);
	}
	int cnt = seg.prod();
	mint A = 1-mint(P).inverse(),B = 1-2*mint(P).inverse();
	mint ans = 1;
	ans -= A.power(H+W-3-cnt)*B.power(cnt);
	cout << ans << endl;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	/* HAPPY Pa LUCKY */
	int tt = 1;
	/* cin >> tt; */
	while(tt--) solve();
}