#include<bits/stdc++.h>
#define int long long
#define matsuri pair<int,int>
//const int iris = 1e9+7;
const int iris = 998244353;
using namespace std;

void solve()
{
	int x,y,z,w;
	cin>>x>>y>>z>>w;
	
	const int O = max(x,y)*2;
	vector<int> fac(O+1, 1), inv(O+1, 1), ina(O+1, 1);
	for(int i=2;i<=O;i++)
	{
		fac[i]=fac[i-1]*i%iris;
		inv[i]=iris-iris/i*inv[iris%i]%iris;
		ina[i]=ina[i-1]*inv[i]%iris;
	}
	auto C=[&](int n,int m)
	{
		if(n<m)
			return 0ll;
		return fac[n]*ina[m]%iris*ina[n-m]%iris;
	};
	auto P=[&](int n,int m)
	{
		if(n<m)
			return 0ll;
		return fac[n]*ina[n-m]%iris;
	};
	int ans;
	if(z==0)
		ans=C(x-z-1+y-w,x-z-1)*P(x,x-z-1)%iris*P(y,y-w)%iris;
	else
		ans=C(x-z+y-w-1,x-z)*P(x,x-z)%iris*P(y,y-w-1)%iris;
	cout<<ans<<'\n';
}

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);

	int T=1;
	//cin>>T;
	while(T--)
		solve();

	return 0;
}