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

using mint = modint998244353;

int main(){
    int h,w,a,b;
    cin >> h >> w >> a >> b;
    mint ans0 = 0;
    for(int i = 0;i < h;i++){
        int l = max(0,i-a+1);
        int r = min(h-a,i);
        mint ad = mint(r-l+1)/(h-a+1);
        ad *= ad;
        ans0 += ad;
    }
    mint ans1 = 0;
    for(int i = 0;i < w;i++){
        int l = max(0,i-b+1);
        int r = min(w-b,i);
        mint ad = mint(r-l+1)/(w-b+1);
        ad *= ad;
        ans1 += ad;
    }
    mint ans = ans0*ans1;
    ans = 2*mint(a)*mint(b)-ans;
    cout << ans.val() << endl;
}