#include<iostream>
#include<cassert>
#include<atcoder/modint>
using namespace std;
using mint=atcoder::modint998244353;
mint f(int H,int A)
{
	mint ret=0;
	for(int k=1;k<A;k++)
	{
		int w=2*A-k;
		if(w>H)continue;
		ret+=mint(k)*(H-w+1)*2;
	}
	ret+=mint(A)*(H-A+1);
	mint t=(H-A+1);
	t*=t;
	return ret/t;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int H,W,A,B;
	cin>>H>>W>>A>>B;
	mint ans=mint(A)*B*2;
	ans-=f(H,A)*f(W,B);
	cout<<ans.val()<<endl;
}