#include <iostream>
using namespace std;

#include <atcoder/modint>
using mint = atcoder::modint998244353;

mint calc(int H, int A) {
    mint ret = 0;
    for (int i = 0; i < H; ++i) {
        int lo = max(i - A + 1, 0), hi = min(i, H - A);
        ret += mint(hi - lo + 1).pow(2);
    }
    return ret / mint(H - A + 1).pow(2);
}

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    int H, W, A, B;
    cin >> H >> W >> A >> B;

    cout << (mint(A) * B * 2 - calc(H, A) * calc(W, B)).val() << '\n';
}