#include <bits/stdc++.h>
#include <atcoder/modint>
using namespace std;
using ll = long long;
using mint = atcoder::modint998244353;

int H, W, A, B;
int main(void){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    cin >> H >> W >> A >> B;
    mint h = 0, w = 0;
    for(int i = 1;i <= H;i++){
        mint p = min(H - A + 1, i) - max(1, i - A + 1) + 1;
        mint q = H - A + 1;
        mint v = p / q;
        h += v * v;
    }
    for(int i = 1;i <= W;i++){
        mint p = min(W - B + 1, i) - max(1, i - B + 1) + 1;
        mint q = W - B + 1;
        mint v = p / q;
        w += v * v;
    }
    mint ans = mint::raw(2) * A * B - h * w;
    cout << ans.val() << endl;
    return 0;
}