#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for(int i=0;i<(int)(n);i++)

// combination MOD
const int MOD=998244353;
const int MAX_N=2e6;
vector<ll> fac(MAX_N+1,1);
vector<ll> finv(MAX_N+1,1);
vector<ll> inv(MAX_N+1,1);
void comb_setup(){
	for(int i=2;i<=MAX_N;i++){
		fac.at(i)=(fac.at(i-1)*i)%MOD;
		inv.at(i)=MOD-(inv.at(MOD%i)*(MOD/i))%MOD;
		finv.at(i)=(finv.at(i-1)*inv.at(i))%MOD;
	}
}
ll comb(int n,int k){
	if(n<k) return 0;
	return fac.at(n)*(finv.at(n-k)*finv.at(k)%MOD)%MOD;
}

int main(){
	comb_setup();
	int x,y,z,w;
	cin>>x>>y>>z>>w;
	if(z==0){
		swap(x,y);
		swap(z,w);
	}
	cout<<((fac.at(x+y-z-w-1)*finv.at(x-z)%MOD*finv.at(y-w-1)%MOD)*comb(x,x-z)%MOD*fac.at(x-z)%MOD*fac.at(y-w)%MOD)<<endl;
}