#include <atcoder/all>
#include <bits/stdc++.h>
using ll = long long;
using ull = unsigned long long;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define REP(i, m, n) for(int i = (int)(m); i < (int)(n); i++)
using namespace std;
using namespace atcoder;
using mint = modint998244353;
const int inf = 1000000007;
const ll longinf = 1ll << 60;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int h, w, a, b;
    cin >> h >> w >> a >> b;
    mint ret = 1;
    rep(_, 2) {
        mint x = 0;
        rep(i, h - a + 1) {
            mint l = min(i, a);
            mint r = min(h - a - i, a);
            x += l * a - l * (l + 1) / 2;
            x += r * a - r * (r + 1) / 2;
            x += a;
        }
        ret *= x / (h - a + 1) / (h - a + 1);
        swap(a, b);
        swap(h, w);
    }
    mint ans = mint(2) * a * b - ret;
    cout << ans.val() << endl;
    return 0;
}