#include<bits/stdc++.h>
using namespace std;

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

int main(){
	ll h, w, a, b; cin >> h >> w >> a >> b;

	vector<mint> imos_h(h+1);
	vector<mint> imos_w(w+1);

	rep(i,0,h-a+1){
		imos_h[0] += 1;
		imos_h[h-a+1-i] -= 1;
		imos_h[1] += 1;
		imos_h[i+1] -= 1;
	}

	rep(i,0,w-b+1){
		imos_w[0] += 1;
		imos_w[w-b+1-i] -= 1;
		imos_w[1] += 1;
		imos_w[i+1] -= 1;
	}

	rep(i,0,h) imos_h[i+1] += imos_h[i];
	rep(i,0,w) imos_w[i+1] += imos_w[i];
	
	mint ans = mint(2) * a * b * mint(h-a+1).pow(2) * mint(w-b+1).pow(2);


	mint hh = 0, ww = 0;
	rep(i,0,a+1){
		hh += mint(a-i) * imos_h[i];
	}
	rep(i,0,b+1){
		ww += mint(b-i) * imos_w[i];
	}
	ans -= hh * ww;

	ans /= mint(h-a+1).pow(2);
	ans /= mint(w-b+1).pow(2);
	cout << ans.val() << '\n';
}