#include <bits/stdc++.h>

#include <atcoder/all>
#define rep(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
using namespace std;
using namespace atcoder;

typedef long long ll;
using mint = modint998244353;

ll g(ll n, ll l) {
    if (n < l) return 0;
    if (n - l + 1 < 0) return 0;
    return n - l + 1;
}

mint f(ll n, ll l) {
    mint ret = 0;
    rep(i, 1, l) { ret += (mint)g(n, 2 * l - i) * 2 * i; }
    ret += g(n, l) * l;
    ret /= g(n, l);
    ret /= g(n, l);
    return ret;
}

int main() {
    ll h, w, a, b;
    cin >> h >> w >> a >> b;
    mint ans = (mint)a * b * 2 - f(h, a) * f(w, b);
    cout << ans.val() << endl;
}