#include <algorithm>
#include <atcoder/modint>
#include <iostream>

using namespace std;
using mint = atcoder::modint998244353;

mint calc(long long h, long long a) {
    mint res = 0;
    mint rev = mint(h - a + 1).inv();
    for (long long i = 0; i < h; i++) {
        int l = max(0ll, i - a + 1);
        int r = min(i, h - a);
        assert(r - l + 1 <= a);
        mint t = (r - l + 1) * rev;
        res += t * t;
    }
    return res;
}

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