#include<bits/stdc++.h>
#include<atcoder/modint>
using namespace std;
using mint=atcoder::modint998244353;
mint P(long L, long K)
{
    mint res=mint(K)*(L-K+1);
    for(int i=1;i<K&&L-K+1-i>=0;i++)res+=2*mint(K-i)*(L-K+1-i);
    res/=L-K+1;
    res/=L-K+1;
    return res;
}
long H,W,A,B;
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>H>>W>>A>>B;
    mint ans=2*mint(A)*B;
    ans-=P(H,A)*P(W,B);
    cout<<ans.val()<<endl;
}